I apologize to be "that guy" but here is my suggestion for you:
1. Reduce your difficulty.
2. You have a skill gap you need to close:
[*] Learn to use crowd control spells to make swarm of enemies practically docile. - that 20+ enemy you can meet within moonrise can controlled with Sleet Storm easily. The same with the Hold the portal for Halshin fight.
[*] Also do you know Cleric is *very* useful in Act 2? They can cast Turn undead, imagine that you cast that spell, in the middle of 500 ghouls?
3. Report the glitch to Larian, I fortunately haven't encounter such weird bug, possibly driver-related issue.
