With the help of @LeonidS we have found out our problem.

It was the wrong command line of the Cron-Job, after correcting this, the updates run without any problems.

We changed the cron command to: /usr/local/bin/ea-php74 /home1/HOSTING/DOMAIN/FOLDER/periodic/cron.php

and let the cron run every minute * * * * *

(This is at shared hosting)