Failed backups in automated backup process

I see in the backup_controllers table 39 courses that failed to backup in the automated backup control process and that ended with status 800. I also see a lot of directories in the temp backup folder that were created during the nightly run of the automated backup process. How can I find out why these backups failed and can I delete these failed backup in the backup_controllers table?

We use Moodle 4.1.9 and the automated backup process runs after 22 hours until next morning.