I forgot to post back that I successfully restored a backup that was not listed correctly on the Hub. It was a fresh backup that I did and the Hub reported (actually still reports) "First backup in progress..." with a filesize of 0 bytes. But i successfuly restored it (migrated it) to a new appliance - no worries.

Actually there were a few things I found during this process, but they are irrelevant to this issue and I have lodged (non-urgent) bug reports.