Yeah but dude.. it happens a lot. Like.. a lot a lot. An overwhelming amount of times that makes it not normal and something is off. I've also noticed that some enemies get to just run by a melee-engaged party member with no opportunity attack, despite not using disengage. Like, it just doesn't trigger half the time. And the AI still overwhelmingly targets and optimizes a strat against low AC/critical party members, cleric and rogue being the most common. My first playthrough I had one hell of a time keeping Astarion and Shadowheart alive, they would just get ganged up on immediately no matter how I placed them or tried to funnel the flow of enemy approach.
I did notice some AoO not triggering, though I know it is only once per turn.
And yes the AI tends to focus the cleric I noticed, and she has mediocre AC (at level 4, I gave her 10 Dex and gave her a half-plate which is Medium armor).
