I'm not sure why AoO isn't working properly, as it works perfectly fine in DoS /shrug. It's just a coding glitch that needs fixing. The attack should take place on the 1st enemy that provokes it - also not sure why you should be able to choose when to use it, as that is just slowing down combat even more for no apparent reason.
"For no apparent reason"? Did you read the OP? If some random goblin eats up my reaction by triggering an AoO, that means I can't use Hellish Rebuke when the boss hits me. That should be a
choice that I make. Reactions are a limited resource, especially ones that spend spell slots or superiority dice. It's incredibly bad design to just have it go off automatically at the first available opportunity.
