Log rotation for a domain is setup to rotate logs by size, but
error_log file occupies too much space and not being rotated upon reaching the configured size.
Log rotation is performed by the Daily Maintenance script. This task will rotate a log file in case if its size is equal or larger than configured. So if the size of log file exceeds a particular limit, but the Daily Maintenance is not started yet then log file will not be rotated (until Daily Maintenance has started).
Configure a cron task to rotate logs for affected domain individually:
Create a crontask with similar content:
01 01,05,10,15,20 * * * /usr/local/psa/logrotate/sbin/logrotate /usr/local/psa/etc/logrotate.d/example.com -s /usr/local/psa/var/logrotate.status
After that log rotation will be performed 5 times a day for the domain 'example.com'.