This is a note to self since the fix is so bizarre and hard to track down. I recently broke bluetooth badly on my Mac Mini which is running Lubuntu 18.04, and took several hours to fix.
Whilst playing with various bluetooth tools I managed to break bluetooth such that nothing bluetooth related worked any more. After lots of reinstalls of software, reboots, and reading random internet web posts on the subject still I had no joy.
Essentially it came down to this - running the command hciconfig dev returned a bluetooth adapter with a corrupt BT address of 00:00:00:00:00:00.
The Fix
Finally, in desperation, I ran the the command sudo service dbus stop which instantly crashed my computer.
However, once I rebooted the computer the bluetooth adapter was recognised as having a valid address, and has worked perfectly ever since.
Don’t you just love computers!