Usually re-pairing is not required. Latest connection is stored in the keyboard and in LE below /storage/.config/bluetooth/. Do you boot "live" or "run"?
Was not included inLE10 and LE11, so likely not required. But just do the simple test and the question is finally answered.
I use the "run" option. Every image build is written freshly to the USB stick. I don't use SFTP/update
Indeed the option --enable-hid2hci is likely not required. I can't hurt to try. As you say, the question will be finally answered.
Will start a fresh bisect process with the mentioned test procedure. I'll keep posting the results.
Thanks a lot so far.