I ran into this bug last night too and was really bummed, but I found a workaround for it similar to the Raedric's Hold workaround.
Basically, the game is trying to transition to the southern bridge area (it's too early in the day for me to be able to spell the name) and failing for some reason - so I went to the save game (on Windows it'll be in (system drive):\Users(your username)\Saved Games\Pillars of Eternity), and open the save game file up with a program like 7zip. Then look for both files with the name Bridge District in them and delete them from the archive, then load the game and try the act transition again, it should spawn you on the south side of the bridge.
If it does work, be sure to backtrack partway across the bridge before you leave - in my game a rather important conversation with Aloth triggered there, there might be others as well if you were meant to spawn just outside the gates and cross the bridge on foot.
