I just upgraded my main server from 6beta12 to 6rc1. I stopped my 4 dockers before upgrading (not sure if I needed to, but made sense to do so) via the unRAID GUI. All seems to have gone well. Will upgrade my backup server next time I power it up.
I rebooted after the upgrade (like I was prompted to do). Under Settings, I went to start Docker and see this message "Your existing Docker image file needs to be recreated due to an issue from an earlier beta of unRAID 6. Failure to do so may result in your docker image suffering corruption at a later time." There is a checkbox to delete the docker image file, so I clicked it then apply. The message is still displayed... but I was able to start Docker and all my Docker Containers fine... and all are running like before. The warning message is still displayed. I suspect this may be covered elsewhere (perhaps would not have shown up if I had upgraded each time a new beta came out)? I will search for it later, but thought I would share that everything seems to be good.
Thanks for all the work that has gone into this!