503 error on user websites caused by CageFS
Check the logs
tail /var/log/apache2/stderr.logFri Apr 29 12:32:02 2022 (95855): Fatal Error Unable to create lock file: Bad file descriptor (9)
To fix the issue follow this guide: Apache: Fatal Error Unable to create lock file: Bad file descriptor (9)
Disable CsageFS for that user:
/usr/sbin/cagefsctl --disable $username
and enable it back:
/usr/sbin/cagefsctl --enable $username
