It just happened to me as soon as I got to Rivington. Main character walking, and the companions just stop following, they’re frozen. I look around and all the NPCs are frozen, then main character freezes and the game just freezes. If I restart or reload they’ll move for like 2 seconds BUT when I reach wyrm rock bridge the game has a brain fart, gets stuck and dies.
This is precisely what loads of folks have been reporting for a while now - myself included.
While it has gotten better for me after hotfix 11, it is still very much a thing (I'm on a PC).
Not so much while running around the city or teleporting using waypoints (although it does happen there too, still) - most annoying is the fact that this seems to happen before any major fight I've done so far in Act III.
- counting house Stone Lord fight - game hung for at least one minute, probably longer, before pre-fight cutscene started
- Cazador fight - a minute or two of wait time before I could do anything. This was more like how lag happens in the city for me, meaning my selected character could still walk around but everybody else is frozen.
- House of Grief fight: Not too pronounced and actually quite playable
- Orin fight at the Bhaal-Temple: Probably the longest wait time of all. Game froze upon opening the inner temple door leading to the main chamber. Probably a minute or two here. After that (exploring the inner temple, talking to Orin's mom and to Orin, start of the fight) ran pretty much as normal.
EDIT: Just started the House of Hope sub-quest but only got as far as talking to Hope for the first time (and preparing the final fight location for Barrelmancy ..

) before I went to bed last night. So far, everything worked flawlessly.
In the city itself, the game will sometimes still freeze when changing between certain locations on foot and/or when fast-traveling to a waypoint. Some waypoints seem more susceptible to this than others and some sub-areas also seem to trigger this more often. For example: Walking back from Dandalon's towards the south will cause lag for me when the party reaches that underpass.
Leaving camp will also sometimes result in companions being stuck in their last camp animation for a while (like SH kneeling in prayer) before everything starts to work as it should. It's not as bad (for me) as it used to be right after patch 4 dropped, but it can still be very frustrating and it seriously disrupts the flow of the game when it gets really bad.
S.