If your source computer is a Mac and the backup job ran initially when the USB drive was attached, then again when it as NOT attached, you may be running into this:
I have a Mac on which there are two backups - one to a remote SFTP destination and one to a not-always-plugged-in USB drive. Both are scheduled to run daily.
The SFTP job runs just fine but I’ve been fighting with the USB destination for weeks now, however I think I finally figured out what was going on so I thought I’d share in case others have insight or similar experiences.
On initial backup creation while the USB drive was connected I set the destination to /Volumes/Backups/Duplicati. Th…