were all your apps up to date?
All but 4 apps were up to date
And Gadgetbridge repeatedly complained that it couldn't connect?
Did you have any other bluetooth options set like a Pin code?
Yes I have a pincode
I guess you might have hit that (but unpairing/repairing should have fixed it).
Probably, I haven't tried repairing indeed.
was that when updating using https://banglejs.com/apps/?id=fwupdate ?
I tried updating to v2.19 again (all apps up-to-date), same issue, infinite 'BOOTING...' loop again... :-(
Then I tried it again after removing the pincode and that worked.
I'm now wondering whether the pincode functionality works at all?