My group of 3 still hasn't ever been able to play the last third of the game since release last year because of this issue, sadly. We keep retrying every month or so and It always happens to us as soon as any 3rd person joins, and only in Lower City. Restarting a campaign, reinstalling, changing host, and changing the SSD Load setting didn't help. Really hope we can still play Act 3 as a group someday.
