>>265784464
I haven't checked for those issues too much (since at this point i'm used to lying down in positions that prevent chest spinning), but i feel like it was much more stable in general, so it might contain the solution for your problem. 

Here's the armature in .fbx, feel free to try aligning yours in similar manner. No idea if it'll help, but it's probably worth a try.
https://file.io/HOkO7C