Loss of internet connectivity?
My local backups are definitely working... like yours, which is mostly what I am relying on, exporting them to a local rpi.
May be one for support? @bobbyD? (and I'll try and remember to use the support tag eventually... )
There are 2 instances when a cloud backup may be missed. Loss of connectivity as @aaiyar suggested or a Z-Wave mesh issue. If you are not sure why your backups are missed, you can send me a PM with your hub's MAC address and will take a look.