The achievement “Leave No Survivors” can not always be completed due to the enemy npc “Veteran Assassin” at one of the traps either spawning inside the wall or the ground and then disappearing making this traps impossible to complete. This occurred 8 out of the 9 times I attempted this achievement.
Edit: After leaving the map and then returning before entering the story instance again this bug seems to not occur anymore, I’m not sure what caused it to trigger the first 8 or so times I attempted this achievement but after rezoning I did not get the bug again.