Angular FormControl with async validator stays in pending status

I have a Form which is not working correctly when I add an Async Validator without Sync validators.

When I add the async validator together with the sync validators the form works

name: new FormControl(
            '',
            Validators.required,
            this.validate.bind(this)
          ),

but when I remove the sync validator the form no longer works i.e other required controls are not triggering

 name: new FormControl(
                '',
                null,
                this.validate.bind(this)
              ),

here is the validate fn

 private validate(control:AbstractControl):Observable<ValidationErrors> {
return control.valueChanges.pipe(
      debounceTime(500),
      distinctUntilChanged(),

      switchMap((value: boolean) => {
        //some logic
        return of(null);
}

Please not that using first() and take(1) as suggested in some posts is not working . When I add a Validator.required on the sync validators everything works

I was able to fix this after following this thread https://github.com/angular/angular/issues/13200

The solution included returning a null observable when the control is prestine or does not have valueChanges using take(1) to ensure that the returned observable in validate() fn is finite.

    private validate(control:AbstractControl):Observable<ValidationErrors> {
     if (!control.valueChanges || control.pristine) {
          return of(null);
        } else {
    return control.valueChanges.pipe(
          debounceTime(500),
          distinctUntilChanged(),
          take(1),
          switchMap((value: boolean) => {
            //some logic
            return of(null);
    },
}