[Snapshot Pro] Backups Failing to Upload to Hub

Hi There,
A number of our sites seem to be able to create full site local backups but fail when uploading to the hub. Our log is full of the following line, repeated over with different timestamps:
“[snapshot][2020-05-18 18:04:15][Warning] Unable to perform requested system backup, proceeding with builtin”.

We have only used ~50/110 GB of our cloud storage. Help with this would be much appreciated as we aren’t sure what to try next.