Looking again at the test, I see a couple of things you can try first:
:arrow: using AndArgumentsMatch is redundant in this case, as you are not returning value based on arguments. Just omit the call and use WhenCalled with a parameterless delegate.
:arrow: If you want the object's original behavior, but just want to fake out one call, you can create the object normally and fake out that specific call
:arrow: If you don't have access to the object's constructor you can specify Members.CallOriginal in Isolate.Fake.Instance() to achieve similar results.
This would look something like this:
var testSheet = new DMFlowtableSheetClass(); //or any other way to initialize this object
Isolate.WhenCalled(() => testSheet.get_SubFlowtables("")).ReturnRecrusiveFake();
Please let us know if this works.