I just wanted to document this issue for new gitlab-backup users:

When gitlab-backup restore -vupok -go SHA1 has been interrupted, the error message shows up when running again:

E: /srv/slapgrid/slappart6/srv/runner/instance/slappart0/var/backup/abignumberhere_gitlab_backup.tar already exists

Solution: Remove that old file.

Re-running may give another error:

cmd_restore: mkdir /srv/slapgrid/slappart6/srv/runner/instance/slappart0/var/repositories.abignumberhere: file exists

Solution: Remove the tar container (which was re-created) + this folder.