What if after you upgrade to 51 you delete the existing entry for the keyboard in the bluetooth menu and then repair? I vaguely remember some post to the effect that the format of the bluetooth connection database has changed. But I can't find the post now and I may misremember.

The hid and hidp modules disappearing is a symptom, not a cause. The modules should be installed automatically by the bluetooth demon. And for reasons that I don't understand, the bluetooth demon is not starting up configured to do keyboard input.