Hey there
How did the avatar get stuck there, is there any specific way to get an enemy to stick?
This problem happens all the time on our server. I don't know if this is the only cause - but I've seen this problem cause it before. If a player dies and uses a resurrection idol it will sometimes cause the avatar of donn (or just about any other catacomb boss) to glitch and not return to their original spawn spot. Although the player will still get attacked, it allows the player to log in and out and re-generate health and energy without having the boss re-generate theirs. Whether this is caused by resurrection idols or logging in and out I do not know. It could just have an off chance of happening when a player dies - I am still uncertain. I can confirm that I have seen it happen quite a few times though.