Hopefully Iron Gate will do a revamp on the bosses. Many of the bosses have these sorts of issues; particularly with their pathing. Moder is the worst; you can engage her and find the right place and shell just get stuck or shoot the sky half the time. If she is killing you; just keep fighting her it won't be long until some crazy stuff happens and she gets easy to kill. Have her chase you down the mountain and see what happens when she has to deal with the trees.

The same thing happens with the Elder, he usually ends up going into the ocean and getting stuck for some reason. He seems to want to swim, but he doesn't now how to swim; so he just sits their hopelessly gazing out into the ocean....

The best boss IMO the ones that feel more complete, are bonemass and Ygaluth. Their pathing seems to work pretty well. Yagluth is really fun to bring into the Black Forest because he just... destroys... the black forest. Apparently meteors cut trees better than an axe; who knew?