Actually (and confusingly), doing an in-place repair - and, in my case, re-installing the BT driver - works. The unknown device (bthl2cap) is gone, bluetooth working fine. Long process, though.
Not Sure if your problem is resolved
This is the solution for me on two different computers with a Qualcom and Intel Bluetooth that were lost when doing WIndows 10 cumulative updates.
Turn Off Fast Shutdown (Power Settings)
Turn Off USB Suspend (Power Settings)
Uninstall USB Root Hub
Shut down (Not just a reboot... shutdown)
Good Luck to anyone else frustrated with this. Took me months to find a solution online that worked. Install reinstall rollbacks did not work.
I just have to take my hat off to you for this solution.
Like you I have been pulling my hair out with this one having updated a couple of compute sticks from 1709 to 1803 one worked perfectly the other the Wireless adapter dropped out of the networking tab and an unknow device, the Bluetooth, appeared.
The confusion was Bluetooth was up and running successfully on the device.
I followed your instructions and everything is now working as expected. Once I re-enable the wireless adapter.
"That man deserve a DB" if you not a Kiwi from New Zealand and haven't heart this expression look it up 😉
Thanks Again for your insight and for publishing this information.