Cron.php suddenly does not run anymore

I have been running a hosted Nextcloud 21.0.2 with the hoster “all-inkl” for a long time.
These days I got an info from the hoster that my disk space is exhausted.
Then I saw in the backend that the cron.php is not running since 14 days.
This was executed by a systemcron until now.
Now I switched to webcron and called the page (cloud.xxx.de/cron.php).
This runs for a few minutes and is finally confirmed with successful.
But in the trashbin, as well as in the fileversions I see, that nothing happened.
Also the script runs much too long.

I have now updated to 22.2.3 (with an intermediate step over 21.0.7), which unfortunately did nothing.
Interesting: I have another test instance on the same server, but in a different folder with a different subdomain.
There was also the 21.0.2 installed - the cron runs there as usual.
I also updated from 21.0.7 to 22.2.3 - runs fine.

Where could I look for the error?

Logfiles are a good starting point: https://docs.nextcloud.com/server/latest/admin_manual/issues/general_troubleshooting.html#troubleshooting-web-server-and-php-problems

Did the cleanup of trashbin and versions work before? If you have terminal access, you can manuall run the occ-script that manages your setup and clean up the trash bin and versions.