The transition to act 2 left me at a black screen for what seemed like a full minute before the cinematic actually started.

Zima opened a door to an area but the invisible wall stopping me from going through didn't go away. Leaving the zone and returning fixed it. The same thing happened when I got to Mercy's arena.

You activate a waypoint in the Vault of Hope that doesn't exist on the map, so you can't actually go back there. There is another waypoint deeper in the vault according to the map though.