I believe there's a problem with how rejected promises for evaluation errors of non-Cyclic (i.e. Synthetic) Module Records are handled w.r.t. HostPromiseRejectionTracker in
InnerModuleEvaluation ( module, stack, index ):

1. If _module_ is not a Cyclic Module Record, then
  a. Let _promise_ be ! _module_.Evaluate().
  b. Assert: _promise_.[[PromiseState]] is not ~pending~.
  c. If _promise_.[[PromiseState]] is ~rejected~, then
    i. Return ThrowCompletion(_promise_.[[PromiseResult]]).

In case of an evaluation error, this code will just unwrap the promise and throw the error, not notifying any HostPromiseRejectionTracker hook that the promise has been handled. OTOH, Evaluate() (presumably) will have already performed RejectPromise (via IfAbruptRejectPromise) and called HostPromiseRejectionTracker(promise, "reject") since [[PromiseIsHandled]] is false. If my understanding is correct, the promise rejection would thus falsely appear to be unhandled.

This code path isn't actually reachable in the spec as of now, but will be when JSON Modules, and thus Synthetic Module Records, land (i.e. #3391).