Great that you found a solution. I would have done something similar. The various abilities (other than BP_Ability and BP_AbilityBase themselves) are intended mostly as examples. I would generally recommend not to extend these anyway and either create new BP_Ability or BP_AbilityBase child actors or duplicate and modify one of the example abilities (like you did). I find it best not to create a taller class hierarchy than what is necessary.
The core of the problem has eluded me so far, but I have not been able to spend that much time on it yet. I will solve it, though. It does not seem to affect the toolkit a couple of versions ago, so it is likely due to some small quirk introduced in a recent update.