Backup with WP Cron suddenly no longer works

The backup no longer works during an installation. I can schedule the job and it is also displayed, but not executed. There is also no log or error message. When the job is started manually, everything works and the backup is created. Even starting the job manually via the URL does not work.

On other installation on the same server it works super nice. Any idea, what could be the error? Already asked the hoster. he said that the cron jobs on the server worked normally. super strange.