A:
I only ever had this happen once, at least it seems like what you describe. I powered off the keyboard, then I had to go into the Bluetooth Setup on the Galaxy Tab-Pro 12.2, and make it "Forget" the keyboard. They I re-paired the keyboard to the tablet as I did for the initial setup.
I never had the problem again, and I suspect it was caused by something "Updating" in the background while I was using it; however, that's only a guess.