Monster respawn animation bug?
Some mobs like the green wisps stay dead on the ground. They stay there until respawn and the way the respawn happens is what I Believe to be the problem:
The dead mob is suddenly dragged from the dead position where you killed it, to the respawn position as if it flew really fast through your screen, instead of havving the dead one desintegrate and have a new one pop on the respawn location, as if the game was recycling that dead one: givving it life and dragging it to the respawn position.
Saw the same with the Antree