@JB this means that it should have done a delta ( as per the full backup interval ) , but had to fall back to a full for at least one disk
this can happens after a failed transfer, a new disk added and some edge case. This issue was not really visible before the latest release, even if the impacts can be important , saturating network and storage.
We are investigating this ( especially @Bastien-Nollet ) , and expect to have a fix and/or an explanation fast
Are you using "purge snapshot data" option ? Are there anything on the journalctl logs ?