Here are my saves about the situation, however I didn't have a previous save where Ishi had normal health, but I did have one with Eder. Also I cannot post a save from it happening to enemies since you cannot save during combat
I pasted the saves to a dropbox account, hopefully it will do
Pillars of Eternity 2 Saves
I am having the same issue, enemies health bar suddenly disappearing and them becoming immortal. Same thing happened to Ishi and Eder, this is really gamebreaking since I can't continue in the drowned barrows when an enemy goes immortal
Really hope they'll address this soon since I cannot play the game at the moment
Full voice acting would be nice, but I'd also be fine with only main characters being completely voiced. This would make big difference to PoE1, since sometimes the first lines were voiced and the rest was text, and frankly that was a little annoying sometimes.