I've had NPCs, notably IFan and The Red Prince, go completely unresponsive. As in,t hey suddenly stand PERFECTLY STILL, NO MATTER WHAT'S HAPPENING TO THEM and even if you switch to them you can't move them, make them attack, make them use skills, or even make them use items from what I foudn.
The first time this happened, immediately thereafter my game crashed when I tried to load but it was with The Red Prince in combat. The second time it was Ifan right after a combat going towards the boat at the undergroudn / inside of the Fort, and then shortly thereafter it happened again with Ifan again as he walked through a poison and electric bud thing, ending up lost forever inside the cloud and dying and being unretrievable.