"Patrol the area near the Mouth of Torment with Redeemer Kossan" is currently bugged, the event is not spawning new enemies to allow for completion of the event. I have tried killing all of the forged in the area, and letting the forged kill Kossan and his escort, neither fixed the issue. There have been multiple people waiting for this event, as it seems the reward from this event is the last part of the collection, for the achievement (in my case it is the very last item I need for the collection).