The OnStartCombat event is only invoked once at the start of combat. It is only invoked again once an enemy has left its combat state and it then re-enters it. I've been wanting to rework the OnAttack event as it is essentially the same thing as the OnDoDamage event, minus actually dealing damage. What I could do is make OnAttack event OnAttackStart and have this invoked when the current attack animation starts and then invoke a new event called OnAttackEnd once the AI's attack has concluded. The problem with all this is that it can all be handled with an Animation Event. I guess this would make it easier as it wouldn't require making Animation Events for every animation and it could offer some added functionality. I tested this though and it was able to reliably enable and disable a collider as you were trying to do. I think the problem was that OnStartCombat is only called once.