In most versions of the game if you do the 2 other DLC and the full game before Belial you can get to part way through the first section of the DLC and have it lock up as something fails to spawn. This is from the ballooning of the save file and the way the game spawns that objective.

I have had the steam version for a long time and I ran into this after farming to get the best gear in the game. Then I ran into that glitch and I never did finish the DLC. So for those that want to be able to do the DLC fully I suggest doing Belial first.