Understandable why arms and legs arent working, but thinking about it the only idea I have right away for what you can fix would be the head, I assume chest and legs at least is something the mods have to make their own support for? Not sure if this is something thats fixable from yourside.
To your knowledge, does this mod work with Smart Moving? Since both modify the player class (and in fact Smart Moving with the optional Render Player API Enhancer co-opts it for its own), I'm guessing it most likely doesn't, but..
Hmm. Well, it doesn't crash, but appears to not work at all, even for spiders. I thought perhaps it might work for non-humanoid mobs. I used to use Better Animations Collection, but it's long, long, long since abandoned.