Ha, I did the exact same thing (travel to talk to Raphael and Voss and then attempted Lower City). Since I couldn't progress after the latest patch, I took the chance to start another campaign. I hope it gets fixed soon.
It works now (as of last night) and pre-hotfix 7. I'll test a save later with hotfix 7 and edit this comment, but the below is before hotfix 7:
Loaded a save that I didn't want to go further than. It was already in Lower City. If I traveled to a different region and traveled back to LC, the game would crash. All saves I tried did this. No matter what I did quest wise in those regions, coming back to LC crashed.
Loaded this save exact save. Instead of changing regions to continue a mission, I started another mission by going to the sewers and then traveling around LC chatting with folks. I may have sacrificed a few dozen Baldurians to my God Talos because they kept eyeing me as I looted dead bodies. Saved the game. Traveled to a different region and then traveled back to LC. NO CRASH.
What fixed it? Was it the sacrifice to my God? Or was it triggering other quest updates? No idea. It worked as of last night and I'm happy.
Ninja Edit: You know? I didn't talk to the bank owner before I went off to Wyrm. This time I chatted to him and started that quest in LC. Why that allows me to travel regions now is unknown.