akhliber: I had this same problem when playing last night. Once I have some coffee I'll try to find the link, but I found this mentioned in the Steam forums, and the dev is aware of the bug... for the time being, the way around it is this:
You must reload to an earlier point (prior to entering the UB) and DO NOT SAVE while in the UB. Just load in, do all your stuff, and get to your team without using the "save" feature. No "quick save" either. Once you get to your team, they'll respond to you and enter the building when you open the door, and then you can enter the Inner Sanctum with your team.
Playing patch 1.2.7, and I also had this problem just now (first time playing in over 6 months). That 'fix' does not work for me: haven't saved at all inside the Brotherhood.
And it
still locks up at the bug fight.
I've seen the Steam Workshop thread too, when I went looking for a workaround. That they are aware of it and it continues to exist is incredible: the bug-fight freeze is a game-breaker - you can't skip that mission, and it seems (in six playthroughs here) to always happen at the exact same spot.