Other users have reported that Déjà Dup repeatedly prompts for the passphrase over a GPG error (although not necessarily the same as yours) during incremental backups, and only successfully completes full backups. See the following bug report and add duplicate status if appropriate.
https://bugs.launchpad.net/ubuntu/+source/deja-dup/+bug/989750 ** Package changed: deja-dup (Ubuntu) => deja-dup -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1540286 Title: deja-dup asks for passphrase over and over again when doing incremental backup, never completes To manage notifications about this bug go to: https://bugs.launchpad.net/deja-dup/+bug/1540286/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs