Did you let Duplicati do an automatic upgrade, or did you install new qnapclub QPKG?
What sort of earlier Duplicati versions were run? Do you know if you ran them as root?
On some NAS systems, root user has little space, and many updates may fill partition.
Downgrading / reverting to a lower version shows where Duplicati autoupdates may be.
The -r usually requests a recursive folder search If so, omit that for process searches.