I already opened a support ticket and they seemed to have it fixed. The "Check OS Snapshot issue" stop showing and now I've regained the option to re-register on Connect. I didn't have to restart unraid-api, reinstall connect plugin or reboot the server. I just tried again, as suggested by Support and everything went fine. Hope this helps you, guys.
Similar problem with recent update. I'm unable to log in to Connect, API running after several restarts But no trace of Flash backup status nor sing out button I've tried uninstalling plugin, rebooting and reinstalling without success.