takeUtil not work in network TIMEOUT workflow

[mydearxym]

when this.stop$ been called, the takeUtil operator not cancel the ajax request as expected.

see details in source file

    this.mutate$ = this.mutateInput$.pipe(
      debounce(() => timer(300)),
      switchMap(q =>
        mutatePromise(q).pipe(
          timeoutWith(TIMEOUT_THRESHOLD, TimoutObservable),
          takeUntil(this.stop$)
        )
      )
    )