main/syslog-ng: logrotate skipped because of dual entry for /var/log/messages
The file /etc/logrotate.d/syslog-ng contains the line /var/log/messages. Because this file is also included in the default /etc/logrotate.conf, logrotate will throw an error and skip the syslog-ng file.
The solution is to comment / remove the line in either of both files.