Yes, I have some of your problems also. I once had bluetooth headphones connected in 8.1, but after trying to repair them they will not install.
I have an image made with fresh install I could try, but no use if the bluetooth problems appear again.
Right now I finally was able to pair my bluetooth keyboard, but does not look like I can have two Bt devices connected together.
edit..
It could also be interference or something
I took my mini pc to another room and I was able to pair bluetooth headphones, phone and keyboards.
Took it back and positioned it half a meter away from where it was and the paired devices work, for now....