I just ran a (full) backup (on a new machine) and it showed up in the Hub straight away. So not at all clear what/where the problem is (I haven't tried doing a new backup of an existing server yet).

I'm hoping one of the core devs will be along shortly to try to have a look at this. Perhaps even to clarify whether or not this is a major issue (ie backups not propagating to Hub and therefore dificult to restore if need be - and they need to get straight onto it) or only a minor issue (ie backups still ok, but just Hub not updating properly - but will catchup soon and/or they will fix when they have time).

[update] I suspect that this is related to this bug registered recently on the bug tracker.