Update: I reloaded a save from before the fight in which Astarion became incapacitated and repeated the encounter, unfortunately reproducing the same error. Shadowheart cast Hold on He Who Was, and Astarion killed him with a flurry of crits--and once again can't move. Astarion was main-handing Knife of the Undermountain and had Shortsword of First Blood in his off-hand. I'm not sure if it was something to do with the particular fight (a cutscene that didn't materialize?) or the behavior of the knife when attacking a held character. Or something that hasn't occurred to me.
Second update: I reloaded again and repeated the fight for a third time. I still had Shadowheart cast Hold, but didn't allow Astarion to use his melee weapons. There was no cutscene after the fight, but Astarion didn't freeze. It could be just an issue with a dual-wielding rogue, but I suspect it's to do with the crit calculations for the Knife combined with a held enemy.
Last edited by Imryll; 17/09/23 08:59 PM.