I created this account to simply echo my experience post patch 4 and add to the other voices that I have seen in hopes there is a fix. I have not seen widespread discussion on this

I'm on PC, steam version

Since patch 4, the entire environment in Act III is shut down � companions do not follow Tav, NPCs walk in place or completely vanish, unable to interact with anyone or anything, unable to select different companions, cannot save, and cannot reload. The lag will resolve for about 15 seconds every 10 minutes. This is a profound problem and extremely unfortunate that this happened. Please fix this asap Larian.