Nextcloud VM System Restore

I just started a System Restore with the System Restore-Script. It asked me to make a system backup beforehand. This backup was successfull. Then I choosed a Backup to restore from the List and at the end of the restore there was a error-message “Something failed while restoring the system partition”. I tried it several Times with different backups, always ending in this error.
Nextcloud then was in Maintenance Mode and I could only turn it off after rebooting the System.
How can I get rid of this error?

Which system (Hardware, operating system, etc.) Disable Maintenance Mode in config.php?

I’m going to try a fresh install, so this Post is obsolete.