We should make a post in Gameplay or support section describing this workaround, to link it to anyone affected (gonna start merging these reports soon).
@Nikia, I doubt this has to do with ACE or with how ACE was integrated (I think, but I might be wrong).
It should be related to some other fixes (we replaced an assertion with a log in hopes it would let the game proceed, but sadly it seems that it does get into a bad state).
If anyone has a reliable way to repro, like, they can see exactly the moment when the hearthling goes missing, please tell us. So far players have reported that the high ipf started happening while in combat.