This morning after having tested that the new version gallery problem was indeed 'fixed' by returning to the previous stable, I wanted to upgrade to RC and again I see the lack of upgrade channels. For screenshot see https://forums.ubports.com/post/95155 . This may be a new problem, or not. I have never wanted to switch back and forth like that previously.
Edit: I restarted the phone again and the channels were back to normal. This is a transient problem.
Edit 2: checking again, the Update parameters screen is displaying 'Channel: candidate', the system state displays '1.2' and checking updates says that everything is up-to-date. This is a bit messed up
Edit 3: after 2 hours of trying of updating, failing, restarting, switching channel, restarting, failing, I finally discovered in a flash of insight into the minds of advanced developers that the update process is actually testing the update history, the things that are displayed below 'recent updates', and this case of getting RC and stable back and forth has never been really thought to be possible (after all, regressions are something that have never been seen for more than one time or two in all the eons of software development), and so unlocking the switch to RC again needed to delete the previous update history.
So I'm finally on RC3 again. Oups, edit 4: RC2