The same problem on my Synology NAS.
My hourly scheduled backup task sometimes completes succesfully, but about 30% of the time the status "Success*". A lot files are skipped, most of the time it's a round number of files: "Files failed to backup: 1000".
I already opened a ticket at the idrive support, but did NOT get any reply.
Hopefully this will be fixed soon because a backup has to be 100% reliable!
Or a backup is succesfull or it fails, nothing in between.