Everytime doing this in the past. The unstable mob has been afflicted by lag. He warps ahead and back as he runs. Some of the changes seem to have fixed that and he runs fast to the tank. So that's nice. However, the same thing seems to have made the custodian healer mob much faster in his run to the dragon. Makes it much harder to get them all dead if going for the achievement or just killing a few to make things quicker.
