Long time, no post. Now running KDE Neon on my desktop and added a USB dongle. When ever I turned off bluetooth I could not turn it back on using the GUI. I found the "btusb" module was not loaded, so a:
sudo modprobe btusb
Solved that. I figured it might be permissions that didn't alllow me to turn bluetooth back on. Sure enough, I was not in the "bluetooth" group.