diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index 1dc4431ad..7cf4979e6 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -25,6 +25,9 @@
     * [Manage Database Users using OIDC](https://www.mongodb.com/docs/kubernetes/upcoming/manage-users/) # TODO
     * [Authentication and Authorization with OIDC/OAuth 2.0](https://www.mongodb.com/docs/manual/core/oidc/security-oidc/)
 
+## Bug Fixes
+* Fixed an issue where moving a **MongoDBMultiCluster** resource to a new project (or a new OM instance) would leave the deployment in a failed state.
+
 <!-- Past Releases -->
 
 # MCK 1.1.0 Release Notes
diff --git a/controllers/om/automation_config_test.go b/controllers/om/automation_config_test.go
index 69300956e..fdc0d8e18 100644
--- a/controllers/om/automation_config_test.go
+++ b/controllers/om/automation_config_test.go
@@ -1059,7 +1059,7 @@ func TestApplyInto(t *testing.T) {
 }
 
 func changeTypes(deployment Deployment) error {
-	rs := deployment.getReplicaSets()
+	rs := deployment.GetReplicaSets()
 	deployment.setReplicaSets(rs)
 	return nil
 }
diff --git a/controllers/om/deployment.go b/controllers/om/deployment.go
index 188de7ff6..fd7f7f776 100644
--- a/controllers/om/deployment.go
+++ b/controllers/om/deployment.go
@@ -280,13 +280,13 @@ func (d Deployment) AddMonitoringAndBackup(log *zap.SugaredLogger, tls bool, caF
 	d.addBackup(log)
 }
 
-// DEPRECATED: this shouldn't be used as it may panic because of different underlying type; use getReplicaSets instead
+// DEPRECATED: this shouldn't be used as it may panic because of different underlying type; use GetReplicaSets instead
 func (d Deployment) ReplicaSets() []ReplicaSet {
 	return d["replicaSets"].([]ReplicaSet)
 }
 
 func (d Deployment) GetReplicaSetByName(name string) ReplicaSet {
-	for _, rs := range d.getReplicaSets() {
+	for _, rs := range d.GetReplicaSets() {
 		if rs.Name() == name {
 			return rs
 		}
@@ -395,7 +395,7 @@ func (d Deployment) RemoveReplicaSetByName(name string, log *zap.SugaredLogger)
 		return xerrors.New("ReplicaSet does not exist")
 	}
 
-	currentRs := d.getReplicaSets()
+	currentRs := d.GetReplicaSets()
 	toKeep := make([]ReplicaSet, len(currentRs)-1)
 	i := 0
 	for _, el := range currentRs {
@@ -685,7 +685,7 @@ func (d Deployment) ProcessesCopy() []Process {
 
 // ReplicaSetsCopy returns the COPY of replicasets in the deployment.
 func (d Deployment) ReplicaSetsCopy() []ReplicaSet {
-	return d.deepCopy().getReplicaSets()
+	return d.deepCopy().GetReplicaSets()
 }
 
 // ShardedClustersCopy returns the COPY of sharded clusters in the deployment.
@@ -958,7 +958,7 @@ func (d Deployment) getProcessByName(name string) *Process {
 }
 
 func (d Deployment) getReplicaSetByName(name string) *ReplicaSet {
-	for _, r := range d.getReplicaSets() {
+	for _, r := range d.GetReplicaSets() {
 		if r.Name() == name {
 			return &r
 		}
@@ -977,7 +977,7 @@ func (d Deployment) getShardedClusterByName(name string) *ShardedCluster {
 	return nil
 }
 
-func (d Deployment) getReplicaSets() []ReplicaSet {
+func (d Deployment) GetReplicaSets() []ReplicaSet {
 	switch v := d["replicaSets"].(type) {
 	case []ReplicaSet:
 		return v
@@ -997,7 +997,7 @@ func (d Deployment) setReplicaSets(replicaSets []ReplicaSet) {
 }
 
 func (d Deployment) addReplicaSet(rs ReplicaSet) {
-	d.setReplicaSets(append(d.getReplicaSets(), rs))
+	d.setReplicaSets(append(d.GetReplicaSets(), rs))
 }
 
 func (d Deployment) getShardedClusters() []ShardedCluster {
@@ -1052,7 +1052,7 @@ func (d Deployment) findReplicaSetsRemovedFromShardedCluster(clusterName string)
 	clusterReplicaSets := shardedCluster.getAllReplicaSets()
 	var ans []string
 
-	for _, v := range d.getReplicaSets() {
+	for _, v := range d.GetReplicaSets() {
 		if !stringutil.Contains(clusterReplicaSets, v.Name()) && isShardOfShardedCluster(clusterName, v.Name()) {
 			ans = append(ans, v.Name())
 		}
diff --git a/controllers/om/deployment_test.go b/controllers/om/deployment_test.go
index a222cadd6..8f0808dae 100644
--- a/controllers/om/deployment_test.go
+++ b/controllers/om/deployment_test.go
@@ -56,9 +56,9 @@ func TestMergeReplicaSet(t *testing.T) {
 	expectedRs := buildRsByProcesses("fooRs", createReplicaSetProcesses("fooRs"))
 
 	assert.Len(t, d.getProcesses(), 3)
-	assert.Len(t, d.getReplicaSets(), 1)
-	assert.Len(t, d.getReplicaSets()[0].Members(), 3)
-	assert.Equal(t, d.getReplicaSets()[0], expectedRs.Rs)
+	assert.Len(t, d.GetReplicaSets(), 1)
+	assert.Len(t, d.GetReplicaSets()[0].Members(), 3)
+	assert.Equal(t, d.GetReplicaSets()[0], expectedRs.Rs)
 
 	// Now the deployment "gets updated" from external - new node is added and one is removed - this should be fixed
 	// by merge
@@ -66,15 +66,15 @@ func TestMergeReplicaSet(t *testing.T) {
 
 	d.getProcesses()[0]["processType"] = ProcessTypeMongos                            // this will be overriden
 	d.getProcesses()[1].EnsureNetConfig()["MaxIncomingConnections"] = 20              // this will be left as-is
-	d.getReplicaSets()[0]["protocolVersion"] = 10                                     // this field will be overriden by Operator
-	d.getReplicaSets()[0].setMembers(d.getReplicaSets()[0].Members()[0:2])            // "removing" the last node in replicaset
-	d.getReplicaSets()[0].addMember(newProcess, "", automationconfig.MemberOptions{}) // "adding" some new node
-	d.getReplicaSets()[0].Members()[0]["arbiterOnly"] = true                          // changing data for first node
+	d.GetReplicaSets()[0]["protocolVersion"] = 10                                     // this field will be overriden by Operator
+	d.GetReplicaSets()[0].setMembers(d.GetReplicaSets()[0].Members()[0:2])            // "removing" the last node in replicaset
+	d.GetReplicaSets()[0].addMember(newProcess, "", automationconfig.MemberOptions{}) // "adding" some new node
+	d.GetReplicaSets()[0].Members()[0]["arbiterOnly"] = true                          // changing data for first node
 
 	mergeReplicaSet(d, "fooRs", createReplicaSetProcesses("fooRs"))
 
 	assert.Len(t, d.getProcesses(), 3)
-	assert.Len(t, d.getReplicaSets(), 1)
+	assert.Len(t, d.GetReplicaSets(), 1)
 
 	expectedRs = buildRsByProcesses("fooRs", createReplicaSetProcesses("fooRs"))
 	expectedRs.Rs.Members()[0]["arbiterOnly"] = true
@@ -89,14 +89,14 @@ func TestMergeReplica_ScaleDown(t *testing.T) {
 
 	mergeReplicaSet(d, "someRs", createReplicaSetProcesses("someRs"))
 	assert.Len(t, d.getProcesses(), 3)
-	assert.Len(t, d.getReplicaSets()[0].Members(), 3)
+	assert.Len(t, d.GetReplicaSets()[0].Members(), 3)
 
 	// "scale down"
 	scaledDownRsProcesses := createReplicaSetProcesses("someRs")[0:2]
 	mergeReplicaSet(d, "someRs", scaledDownRsProcesses)
 
 	assert.Len(t, d.getProcesses(), 2)
-	assert.Len(t, d.getReplicaSets()[0].Members(), 2)
+	assert.Len(t, d.GetReplicaSets()[0].Members(), 2)
 
 	// checking that the last member was removed
 	rsProcesses := buildRsByProcesses("someRs", createReplicaSetProcesses("someRs")).Processes
@@ -123,7 +123,7 @@ func TestMergeReplicaSet_MergeFirstProcess(t *testing.T) {
 	mergeReplicaSet(d, "fooRs", createReplicaSetProcessesCount(5, "fooRs"))
 
 	assert.Len(t, d.getProcesses(), 8)
-	assert.Len(t, d.getReplicaSets(), 2)
+	assert.Len(t, d.GetReplicaSets(), 2)
 
 	expectedRs := buildRsByProcesses("fooRs", createReplicaSetProcessesCount(5, "fooRs"))
 
@@ -177,8 +177,8 @@ func TestMergeDeployment_BigReplicaset(t *testing.T) {
 	checkNumberOfVotingMembers(t, rs, 7, 8)
 
 	// Now OM user "has changed" votes for some of the members - this must stay the same after merge
-	omDeployment.getReplicaSets()[0].Members()[2].setVotes(0).setPriority(0)
-	omDeployment.getReplicaSets()[0].Members()[4].setVotes(0).setPriority(0)
+	omDeployment.GetReplicaSets()[0].Members()[2].setVotes(0).setPriority(0)
+	omDeployment.GetReplicaSets()[0].Members()[4].setVotes(0).setPriority(0)
 
 	omDeployment.MergeReplicaSet(rs, nil, nil, zap.S())
 	checkNumberOfVotingMembers(t, rs, 5, 8)
@@ -199,10 +199,10 @@ func TestMergeDeployment_BigReplicaset(t *testing.T) {
 
 	omDeployment.MergeReplicaSet(rsToMerge, nil, nil, zap.S())
 	checkNumberOfVotingMembers(t, rs, 7, 11)
-	assert.Equal(t, 0, omDeployment.getReplicaSets()[0].Members()[2].Votes())
-	assert.Equal(t, 0, omDeployment.getReplicaSets()[0].Members()[4].Votes())
-	assert.Equal(t, float32(0), omDeployment.getReplicaSets()[0].Members()[2].Priority())
-	assert.Equal(t, float32(0), omDeployment.getReplicaSets()[0].Members()[4].Priority())
+	assert.Equal(t, 0, omDeployment.GetReplicaSets()[0].Members()[2].Votes())
+	assert.Equal(t, 0, omDeployment.GetReplicaSets()[0].Members()[4].Votes())
+	assert.Equal(t, float32(0), omDeployment.GetReplicaSets()[0].Members()[2].Priority())
+	assert.Equal(t, float32(0), omDeployment.GetReplicaSets()[0].Members()[4].Priority())
 }
 
 func TestGetAllProcessNames_MergedReplicaSetsAndShardedClusters(t *testing.T) {
@@ -360,7 +360,7 @@ func TestGetNumberOfExcessProcesses_ShardedClusterScaleDown(t *testing.T) {
 	_, err := d.MergeShardedCluster(mergeOpts)
 	assert.NoError(t, err)
 	assert.Len(t, d.getShardedClusterByName("sc001").shards(), 3)
-	assert.Len(t, d.getReplicaSets(), 4)
+	assert.Len(t, d.GetReplicaSets(), 4)
 	assert.Equal(t, 0, d.GetNumberOfExcessProcesses("sc001"))
 
 	// Now we are "scaling down" the sharded cluster - so junk replica sets will appear - this is still ok
@@ -377,7 +377,7 @@ func TestGetNumberOfExcessProcesses_ShardedClusterScaleDown(t *testing.T) {
 	_, err = d.MergeShardedCluster(mergeOpts)
 	assert.NoError(t, err)
 	assert.Len(t, d.getShardedClusterByName("sc001").shards(), 2)
-	assert.Len(t, d.getReplicaSets(), 4)
+	assert.Len(t, d.GetReplicaSets(), 4)
 
 	assert.Equal(t, 0, d.GetNumberOfExcessProcesses("sc001"))
 }
@@ -586,7 +586,7 @@ func checkShardedClusterCheckExtraReplicaSets(t *testing.T, d Deployment, expect
 		// checking that no previous replica sets are left. For this we take the name of first shard and remove the last digit
 		firstShardName := expectedReplicaSets[0].Rs.Name()
 		i := 0
-		for _, r := range d.getReplicaSets() {
+		for _, r := range d.GetReplicaSets() {
 			if strings.HasPrefix(r.Name(), firstShardName[0:len(firstShardName)-1]) {
 				i++
 			}
diff --git a/controllers/om/depshardedcluster_test.go b/controllers/om/depshardedcluster_test.go
index e93a90412..e9f025dd0 100644
--- a/controllers/om/depshardedcluster_test.go
+++ b/controllers/om/depshardedcluster_test.go
@@ -31,9 +31,9 @@ func TestMergeShardedCluster_New(t *testing.T) {
 	assert.NoError(t, err)
 
 	require.Len(t, d.getProcesses(), 15)
-	require.Len(t, d.getReplicaSets(), 4)
+	require.Len(t, d.GetReplicaSets(), 4)
 	for i := 0; i < 4; i++ {
-		require.Len(t, d.getReplicaSets()[i].Members(), 3)
+		require.Len(t, d.GetReplicaSets()[i].Members(), 3)
 	}
 	checkMongoSProcesses(t, d.getProcesses(), createMongosProcesses(3, "pretty", "cluster"))
 	checkReplicaSet(t, d, createConfigSrvRs("configSrv", true))
@@ -130,9 +130,9 @@ func TestMergeShardedCluster_ReplicaSetsModified(t *testing.T) {
 	expectedShards[0].Rs["writeConcernMajorityJournalDefault"] = true
 
 	require.Len(t, d.getProcesses(), 15)
-	require.Len(t, d.getReplicaSets(), 4)
+	require.Len(t, d.GetReplicaSets(), 4)
 	for i := 0; i < 4; i++ {
-		require.Len(t, d.getReplicaSets()[i].Members(), 3)
+		require.Len(t, d.GetReplicaSets()[i].Members(), 3)
 	}
 	checkMongoSProcesses(t, d.getProcesses(), createMongosProcesses(3, "pretty", "cluster"))
 	checkReplicaSet(t, d, createConfigSrvRs("configSrv", true))
@@ -166,7 +166,7 @@ func TestMergeShardedCluster_ShardedClusterModified(t *testing.T) {
 
 	mergeReplicaSet(d, "fakeShard", createReplicaSetProcesses("fakeShard"))
 
-	require.Len(t, d.getReplicaSets(), 5)
+	require.Len(t, d.GetReplicaSets(), 5)
 
 	// Final check - we create the expected configuration, add there correct OM changes and check for equality with merge
 	// result
@@ -188,9 +188,9 @@ func TestMergeShardedCluster_ShardedClusterModified(t *testing.T) {
 	// Note, that fake replicaset and it's processes haven't disappeared as we passed 'false' to 'MergeShardedCluster'
 	// which results in "draining" for redundant shards but not physical removal of replica sets
 	require.Len(t, d.getProcesses(), 18)
-	require.Len(t, d.getReplicaSets(), 5)
+	require.Len(t, d.GetReplicaSets(), 5)
 	for i := 0; i < 4; i++ {
-		require.Len(t, d.getReplicaSets()[i].Members(), 3)
+		require.Len(t, d.GetReplicaSets()[i].Members(), 3)
 	}
 	checkMongoSProcesses(t, d.getProcesses(), createMongosProcesses(3, "pretty", "cluster"))
 	checkReplicaSet(t, d, createConfigSrvRs("configSrv", true))
diff --git a/controllers/om/mockedomclient.go b/controllers/om/mockedomclient.go
index d5b90eef9..51c3f844d 100644
--- a/controllers/om/mockedomclient.go
+++ b/controllers/om/mockedomclient.go
@@ -734,7 +734,7 @@ func (oc *MockedOmConnection) CheckResourcesAndBackupDeleted(t *testing.T, resou
 	// This can be improved for some more complicated scenarios when we have different resources in parallel - so far
 	// just checking if deployment
 	assert.Empty(t, oc.deployment.getProcesses())
-	assert.Empty(t, oc.deployment.getReplicaSets())
+	assert.Empty(t, oc.deployment.GetReplicaSets())
 	assert.Empty(t, oc.deployment.getShardedClusters())
 	assert.Empty(t, oc.deployment.getMonitoringVersions())
 	assert.Empty(t, oc.deployment.getBackupVersions())
diff --git a/controllers/om/omclient.go b/controllers/om/omclient.go
index 7ec1336a1..cbc0c2875 100644
--- a/controllers/om/omclient.go
+++ b/controllers/om/omclient.go
@@ -978,6 +978,21 @@ func (oc *HTTPOmConnection) AddPreferredHostname(agentApiKey string, value strin
 	return nil
 }
 
+func GetReplicaSetMemberIds(conn Connection) (map[string]map[string]int, error) {
+	dep, err := conn.ReadDeployment()
+	if err != nil {
+		return nil, err
+	}
+
+	finalProcessIds := make(map[string]map[string]int)
+
+	for _, replicaSet := range dep.GetReplicaSets() {
+		finalProcessIds[replicaSet.Name()] = replicaSet.MemberIds()
+	}
+
+	return finalProcessIds, nil
+}
+
 //********************************** Private methods *******************************************************************
 
 func (oc *HTTPOmConnection) get(path string) ([]byte, error) {
diff --git a/controllers/om/replicaset.go b/controllers/om/replicaset.go
index 7c6ea8ed5..181899a4f 100644
--- a/controllers/om/replicaset.go
+++ b/controllers/om/replicaset.go
@@ -146,6 +146,14 @@ func (r ReplicaSet) String() string {
 	return fmt.Sprintf("\"%s\" (members: %v)", r.Name(), r.Members())
 }
 
+func (r ReplicaSet) MemberIds() map[string]int {
+	memberIds := make(map[string]int)
+	for _, rsMember := range r.Members() {
+		memberIds[rsMember.Name()] = rsMember.Id()
+	}
+	return memberIds
+}
+
 // ***************************************** Private methods ***********************************************************
 
 func initDefaultRs(set ReplicaSet, name string, protocolVersion string) {
diff --git a/controllers/operator/mongodbmultireplicaset_controller.go b/controllers/operator/mongodbmultireplicaset_controller.go
index 11d2daeb2..fc2ccde71 100644
--- a/controllers/operator/mongodbmultireplicaset_controller.go
+++ b/controllers/operator/mongodbmultireplicaset_controller.go
@@ -201,8 +201,13 @@ func (r *ReconcileMongoDbMultiReplicaSet) Reconcile(ctx context.Context, request
 		return r.updateStatus(ctx, &mrs, status, log)
 	}
 
+	finalMemberIds, err := om.GetReplicaSetMemberIds(conn)
+	if err != nil {
+		return r.updateStatus(ctx, &mrs, workflow.Failed(err), log)
+	}
+
 	mrs.Status.FeatureCompatibilityVersion = mrs.CalculateFeatureCompatibilityVersion()
-	if err := r.saveLastAchievedSpec(ctx, mrs); err != nil {
+	if err := r.saveLastAchievedSpec(ctx, mrs, finalMemberIds); err != nil {
 		return r.updateStatus(ctx, &mrs, workflow.Failed(xerrors.Errorf("Failed to set annotation: %w", err)), log)
 	}
 
@@ -627,7 +632,7 @@ func getMembersForClusterSpecItemThisReconciliation(mrs *mdbmultiv1.MongoDBMulti
 }
 
 // saveLastAchievedSpec updates the MongoDBMultiCluster resource with the spec that was just achieved.
-func (r *ReconcileMongoDbMultiReplicaSet) saveLastAchievedSpec(ctx context.Context, mrs mdbmultiv1.MongoDBMultiCluster) error {
+func (r *ReconcileMongoDbMultiReplicaSet) saveLastAchievedSpec(ctx context.Context, mrs mdbmultiv1.MongoDBMultiCluster, rsMemberIds map[string]map[string]int) error {
 	clusterSpecs, err := mrs.GetClusterSpecItems()
 	if err != nil {
 		return err
@@ -657,6 +662,16 @@ func (r *ReconcileMongoDbMultiReplicaSet) saveLastAchievedSpec(ctx context.Conte
 		annotationsToAdd[mdbmultiv1.LastClusterNumMapping] = string(clusterNumBytes)
 	}
 
+	if len(rsMemberIds) > 0 {
+		rsMemberIdsBytes, err := json.Marshal(rsMemberIds)
+		if err != nil {
+			return err
+		}
+		if len(rsMemberIdsBytes) > 0 {
+			annotationsToAdd[util.LastAchievedRsMemberIds] = string(rsMemberIdsBytes)
+		}
+	}
+
 	return annotations.SetAnnotations(ctx, &mrs, annotationsToAdd, r.client)
 }
 
@@ -699,6 +714,15 @@ func (r *ReconcileMongoDbMultiReplicaSet) updateOmDeploymentRs(ctx context.Conte
 	}
 
 	processIds := getReplicaSetProcessIdsFromReplicaSets(mrs.Name, existingDeployment)
+
+	// If there is no replicaset configuration saved in OM, it might be a new project, so we check the ids saved in annotation
+	// A project migration can happen if .spec.opsManager.configMapRef is changed, or the original configMap has been modified.
+	if len(processIds) == 0 {
+		processIds, err = getReplicaSetProcessIdsFromAnnotation(mrs)
+		if err != nil {
+			return xerrors.Errorf("failed to get member ids from annotation: %w", err)
+		}
+	}
 	log.Debugf("Existing process Ids: %+v", processIds)
 
 	certificateFileName := ""
@@ -794,6 +818,17 @@ func getReplicaSetProcessIdsFromReplicaSets(replicaSetName string, deployment om
 	return processIds
 }
 
+func getReplicaSetProcessIdsFromAnnotation(mrs mdbmultiv1.MongoDBMultiCluster) (map[string]int, error) {
+	if processIdsStr, ok := mrs.Annotations[util.LastAchievedRsMemberIds]; ok {
+		processIds := make(map[string]map[string]int)
+		if err := json.Unmarshal([]byte(processIdsStr), &processIds); err != nil {
+			return map[string]int{}, err
+		}
+		return processIds[mrs.Name], nil
+	}
+	return make(map[string]int), nil
+}
+
 func getSRVService(mrs *mdbmultiv1.MongoDBMultiCluster) corev1.Service {
 	additionalConfig := mrs.Spec.GetAdditionalMongodConfig()
 	port := additionalConfig.GetPortOrDefault()
diff --git a/controllers/operator/mongodbmultireplicaset_controller_test.go b/controllers/operator/mongodbmultireplicaset_controller_test.go
index fb9819283..806ace443 100644
--- a/controllers/operator/mongodbmultireplicaset_controller_test.go
+++ b/controllers/operator/mongodbmultireplicaset_controller_test.go
@@ -945,6 +945,90 @@ func TestScaling(t *testing.T) {
 		assertMemberNameAndId(t, members, fmt.Sprintf("%s-2-0", mrs.Name), 2)
 	})
 
+	t.Run("Added members reuse member Ids when annotation is set", func(t *testing.T) {
+		mrs := mdbmulti.DefaultMultiReplicaSetBuilder().
+			SetClusterSpecList(clusters).
+			Build()
+
+		mrs.Spec.ClusterSpecList[0].Members = 1
+		mrs.Spec.ClusterSpecList[1].Members = 1
+		mrs.Spec.ClusterSpecList[2].Members = 1
+		reconciler, client, _, omConnectionFactory := defaultMultiReplicaSetReconciler(ctx, nil, "", "", mrs)
+		checkMultiReconcileSuccessful(ctx, t, reconciler, mrs, client, false)
+
+		assert.Len(t, omConnectionFactory.GetConnection().(*om.MockedOmConnection).GetProcesses(), 3)
+
+		dep, err := omConnectionFactory.GetConnection().ReadDeployment()
+		assert.NoError(t, err)
+
+		replicaSets := dep.GetReplicaSets()
+
+		assert.Len(t, replicaSets, 1)
+		members := replicaSets[0].Members()
+		assert.Len(t, members, 3)
+
+		assertMemberNameAndId(t, members, fmt.Sprintf("%s-0-0", mrs.Name), 0)
+		assertMemberNameAndId(t, members, fmt.Sprintf("%s-1-0", mrs.Name), 1)
+		assertMemberNameAndId(t, members, fmt.Sprintf("%s-2-0", mrs.Name), 2)
+
+		assert.Equal(t, members[0].Id(), 0)
+		assert.Equal(t, members[1].Id(), 1)
+		assert.Equal(t, members[2].Id(), 2)
+
+		rsMemberIds := map[string]map[string]int{
+			mrs.GetName(): {
+				fmt.Sprintf("%s-0-0", mrs.Name): 0,
+				fmt.Sprintf("%s-1-0", mrs.Name): 1,
+				fmt.Sprintf("%s-2-0", mrs.Name): 2,
+			},
+		}
+
+		rsMemberIdsBytes, _ := json.Marshal(rsMemberIds)
+
+		// Assert that the member ids are saved in the annotation
+		assert.Equal(t, mrs.GetAnnotations()[util.LastAchievedRsMemberIds], string(rsMemberIdsBytes))
+
+		// Scaling up this cluster means we get non-sequential member Ids
+		mrs.Spec.ClusterSpecList[0].Members = 2
+
+		checkMultiReconcileSuccessful(ctx, t, reconciler, mrs, client, false)
+
+		dep, err = omConnectionFactory.GetConnection().ReadDeployment()
+		assert.NoError(t, err)
+
+		replicaSets = dep.GetReplicaSets()
+
+		assert.Len(t, replicaSets, 1)
+		members = replicaSets[0].Members()
+		assert.Len(t, members, 4)
+
+		assertMemberNameAndId(t, members, fmt.Sprintf("%s-0-0", mrs.Name), 0)
+		assertMemberNameAndId(t, members, fmt.Sprintf("%s-0-1", mrs.Name), 3)
+		assertMemberNameAndId(t, members, fmt.Sprintf("%s-1-0", mrs.Name), 1)
+		assertMemberNameAndId(t, members, fmt.Sprintf("%s-2-0", mrs.Name), 2)
+
+		// Assert that the member ids are updated in the annotation
+		rsMemberIds[mrs.GetName()][fmt.Sprintf("%s-0-1", mrs.Name)] = 3
+		rsMemberIdsBytes, _ = json.Marshal(rsMemberIds)
+		assert.Equal(t, mrs.GetAnnotations()[util.LastAchievedRsMemberIds], string(rsMemberIdsBytes))
+
+		// We simulate a changing the project by recreating the omConnection. The resource will keep the annotation.
+		// This part would have failed before 1.2.0.
+		reconciler, client, _, omConnectionFactory = defaultMultiReplicaSetReconciler(ctx, nil, "", "", mrs)
+		checkMultiReconcileSuccessful(ctx, t, reconciler, mrs, client, false)
+
+		dep, err = omConnectionFactory.GetConnection().ReadDeployment()
+		assert.NoError(t, err)
+
+		replicaSets = dep.GetReplicaSets()
+		members = replicaSets[0].Members()
+
+		assertMemberNameAndId(t, members, fmt.Sprintf("%s-0-0", mrs.Name), 0)
+		assertMemberNameAndId(t, members, fmt.Sprintf("%s-0-1", mrs.Name), 3)
+		assertMemberNameAndId(t, members, fmt.Sprintf("%s-1-0", mrs.Name), 1)
+		assertMemberNameAndId(t, members, fmt.Sprintf("%s-2-0", mrs.Name), 2)
+	})
+
 	t.Run("Cluster can be added", func(t *testing.T) {
 		mrs := mdbmulti.DefaultMultiReplicaSetBuilder().SetClusterSpecList(clusters).Build()
 		mrs.Spec.ClusterSpecList = mrs.Spec.ClusterSpecList[:len(mrs.Spec.ClusterSpecList)-1]
diff --git a/docker/mongodb-kubernetes-tests/kubetester/mongodb_multi.py b/docker/mongodb-kubernetes-tests/kubetester/mongodb_multi.py
index b35316c32..ab5f867d3 100644
--- a/docker/mongodb-kubernetes-tests/kubetester/mongodb_multi.py
+++ b/docker/mongodb-kubernetes-tests/kubetester/mongodb_multi.py
@@ -3,6 +3,7 @@
 from typing import Dict, List, Optional
 
 from kubernetes import client
+from kubetester import wait_until
 from kubetester.mongodb import MongoDB
 from kubetester.mongotester import MongoTester, MultiReplicaSetTester
 from kubetester.multicluster_client import MultiClusterClient
@@ -77,6 +78,21 @@ def service_names(self) -> List[str]:
                 service_names.append(f"{self.name}-{i}-{j}-svc")
         return service_names
 
+    def assert_statefulsets_are_ready(self, clients: List[MultiClusterClient], timeout: int = 600):
+        def fn():
+            statefulsets = self.read_statefulsets(clients)
+
+            assert len(statefulsets) == len(self["spec"]["clusterSpecList"])
+
+            for i, mcc in enumerate(clients):
+                cluster_sts = statefulsets[mcc.cluster_name]
+                if cluster_sts.status.ready_replicas != self.get_item_spec(mcc.cluster_name)["members"]:
+                    return False
+
+            return True
+
+        wait_until(fn, timeout=timeout, interval=10, message="Waiting for all statefulsets to be ready")
+
     def tester(
         self,
         ca_path: Optional[str] = None,
diff --git a/docker/mongodb-kubernetes-tests/tests/multicluster/multi_cluster_scale_up_cluster.py b/docker/mongodb-kubernetes-tests/tests/multicluster/multi_cluster_scale_up_cluster.py
index f289ea19d..3acc73dff 100644
--- a/docker/mongodb-kubernetes-tests/tests/multicluster/multi_cluster_scale_up_cluster.py
+++ b/docker/mongodb-kubernetes-tests/tests/multicluster/multi_cluster_scale_up_cluster.py
@@ -1,9 +1,18 @@
+from operator import truediv
 from typing import List
 
 import kubernetes
 import pytest
+from kubetester import (
+    create_or_update_configmap,
+    random_k8s_name,
+    read_configmap,
+    try_load,
+    wait_until,
+)
 from kubetester.automation_config_tester import AutomationConfigTester
 from kubetester.certs_mongodb_multi import create_multi_cluster_mongodb_tls_certs
+from kubetester.kubetester import KubernetesTester
 from kubetester.kubetester import fixture as yaml_fixture
 from kubetester.kubetester import skip_if_local
 from kubetester.mongodb_multi import MongoDBMulti
@@ -17,6 +26,26 @@
 BUNDLE_SECRET_NAME = f"prefix-{RESOURCE_NAME}-cert"
 
 
+@pytest.fixture(scope="module")
+def project_name_prefix(namespace: str) -> str:
+    return random_k8s_name(f"{namespace}-project-")
+
+
+@pytest.fixture(scope="module")
+def new_project_configmap(namespace: str, project_name_prefix: str) -> str:
+    cm = read_configmap(namespace=namespace, name="my-project")
+    project_name = f"{project_name_prefix}-new-project"
+    return create_or_update_configmap(
+        namespace=namespace,
+        name=project_name,
+        data={
+            "baseUrl": cm["baseUrl"],
+            "projectName": project_name,
+            "orgId": cm["orgId"],
+        },
+    )
+
+
 @pytest.fixture(scope="module")
 def mongodb_multi_unmarshalled(
     namespace: str,
@@ -28,7 +57,7 @@ def mongodb_multi_unmarshalled(
     resource = MongoDBMulti.from_yaml(yaml_fixture("mongodb-multi.yaml"), RESOURCE_NAME, namespace)
     resource.set_version(custom_mdb_version)
     # ensure certs are created for the members during scale up
-    resource["spec"]["clusterSpecList"] = cluster_spec_list(member_cluster_names, [2, 1, 2])
+    resource["spec"]["clusterSpecList"] = cluster_spec_list(member_cluster_names, [3, 1, 2])
     resource["spec"]["security"] = {
         "certsSecretPrefix": "prefix",
         "tls": {
@@ -56,11 +85,16 @@ def server_certs(
     )
 
 
-@pytest.fixture(scope="module")
+@pytest.fixture(scope="function")
 def mongodb_multi(mongodb_multi_unmarshalled: MongoDBMulti, server_certs: str) -> MongoDBMulti:
+    if try_load(mongodb_multi_unmarshalled):
+        return mongodb_multi_unmarshalled
+
     # remove the last element, we are only starting with 2 clusters we will scale up the 3rd one later.
     mongodb_multi_unmarshalled["spec"]["clusterSpecList"].pop()
-    return mongodb_multi_unmarshalled.update()
+    # remove one member from the first cluster to start with 2 members
+    mongodb_multi_unmarshalled["spec"]["clusterSpecList"][0]["members"] = 2
+    return mongodb_multi_unmarshalled
 
 
 @pytest.mark.e2e_multi_cluster_scale_up_cluster
@@ -70,6 +104,7 @@ def test_deploy_operator(multi_cluster_operator: Operator):
 
 @pytest.mark.e2e_multi_cluster_scale_up_cluster
 def test_create_mongodb_multi(mongodb_multi: MongoDBMulti):
+    mongodb_multi.update()
     mongodb_multi.assert_reaches_phase(Phase.Running, timeout=600)
 
 
@@ -79,14 +114,7 @@ def test_statefulsets_have_been_created_correctly(
     member_cluster_clients: List[MultiClusterClient],
 ):
     # read all statefulsets except the last one
-    statefulsets = mongodb_multi.read_statefulsets(member_cluster_clients[:-1])
-    cluster_one_client = member_cluster_clients[0]
-    cluster_one_sts = statefulsets[cluster_one_client.cluster_name]
-    assert cluster_one_sts.status.ready_replicas == 2
-
-    cluster_two_client = member_cluster_clients[1]
-    cluster_two_sts = statefulsets[cluster_two_client.cluster_name]
-    assert cluster_two_sts.status.ready_replicas == 1
+    mongodb_multi.assert_statefulsets_are_ready(member_cluster_clients[:-1])
 
 
 @pytest.mark.e2e_multi_cluster_scale_up_cluster
@@ -97,7 +125,6 @@ def test_ops_manager_has_been_updated_correctly_before_scaling():
 
 @pytest.mark.e2e_multi_cluster_scale_up_cluster
 def test_scale_mongodb_multi(mongodb_multi: MongoDBMulti, member_cluster_clients: List[MultiClusterClient]):
-    mongodb_multi.load()
     mongodb_multi["spec"]["clusterSpecList"].append(
         {"members": 2, "clusterName": member_cluster_clients[2].cluster_name}
     )
@@ -111,21 +138,7 @@ def test_statefulsets_have_been_scaled_up_correctly(
     mongodb_multi: MongoDBMulti,
     member_cluster_clients: List[MultiClusterClient],
 ):
-    statefulsets = mongodb_multi.read_statefulsets(member_cluster_clients)
-
-    assert len(statefulsets) == 3
-
-    cluster_one_client = member_cluster_clients[0]
-    cluster_one_sts = statefulsets[cluster_one_client.cluster_name]
-    assert cluster_one_sts.status.ready_replicas == 2
-
-    cluster_two_client = member_cluster_clients[1]
-    cluster_two_sts = statefulsets[cluster_two_client.cluster_name]
-    assert cluster_two_sts.status.ready_replicas == 1
-
-    cluster_three_client = member_cluster_clients[2]
-    cluster_three_sts = statefulsets[cluster_three_client.cluster_name]
-    assert cluster_three_sts.status.ready_replicas == 2
+    mongodb_multi.assert_statefulsets_are_ready(member_cluster_clients, timeout=60)
 
 
 @pytest.mark.e2e_multi_cluster_scale_up_cluster
@@ -139,3 +152,42 @@ def test_ops_manager_has_been_updated_correctly_after_scaling():
 def test_replica_set_is_reachable(mongodb_multi: MongoDBMulti, ca_path: str):
     tester = mongodb_multi.tester()
     tester.assert_connectivity(opts=[with_tls(use_tls=True, ca_path=ca_path)])
+
+
+# From here on, the tests are for verifying that we can change the project of the MongoDBMulti resource even with
+# non-sequential member ids in the replicaset.
+
+
+@pytest.mark.e2e_multi_cluster_scale_up_cluster
+class TestNonSequentialMemberIdsInReplicaSet(KubernetesTester):
+
+    def test_scale_up_first_cluster(
+        self, mongodb_multi: MongoDBMulti, member_cluster_clients: List[MultiClusterClient]
+    ):
+        # Scale up the first cluster to 3 members. This will lead to non-sequential member ids in the replicaset.
+        # multi-replica-set-0-0 : 0
+        # multi-replica-set-0-1 : 1
+        # multi-replica-set-0-2 : 5
+        # multi-replica-set-1-0 : 2
+        # multi-replica-set-2-0 : 3
+        # multi-replica-set-2-1 : 4
+
+        mongodb_multi["spec"]["clusterSpecList"][0]["members"] = 3
+        mongodb_multi.update()
+
+        mongodb_multi.assert_statefulsets_are_ready(member_cluster_clients)
+        mongodb_multi.assert_reaches_phase(Phase.Running, timeout=600)
+
+    def test_change_project(self, mongodb_multi: MongoDBMulti, new_project_configmap: str):
+        oldRsMembers = mongodb_multi.get_automation_config_tester().get_replica_set_members(mongodb_multi.name)
+
+        mongodb_multi["spec"]["opsManager"]["configMapRef"]["name"] = new_project_configmap
+        mongodb_multi.update()
+
+        mongodb_multi.assert_abandons_phase(phase=Phase.Running, timeout=300)
+        mongodb_multi.assert_reaches_phase(phase=Phase.Running, timeout=600)
+
+        newRsMembers = mongodb_multi.get_automation_config_tester().get_replica_set_members(mongodb_multi.name)
+
+        # Assert that the replica set member ids have not changed after changing the project.
+        assert oldRsMembers == newRsMembers
diff --git a/pkg/util/constants.go b/pkg/util/constants.go
index 9ed9d94eb..747ca5589 100644
--- a/pkg/util/constants.go
+++ b/pkg/util/constants.go
@@ -283,7 +283,10 @@ const (
 	// TODO: remove this from here and move it to the certs package
 	// This currently creates an import cycle
 	InternalCertAnnotationKey = "internalCertHash"
-	LastAchievedSpec          = "mongodb.com/v1.lastSuccessfulConfiguration"
+
+	// Annotation keys used by the operator
+	LastAchievedSpec        = "mongodb.com/v1.lastSuccessfulConfiguration"
+	LastAchievedRsMemberIds = "mongodb.com/v1.lastAchievedRsMemberIds"
 
 	// SecretVolumeName is the name of the volume resource.
 	SecretVolumeName = "secret-certs"