I guess you have some modification to the postfix configuration (probably to settings for the queue lifetime) - in that case it might be that the setting is too low...
please provide:
* any modifications to the configuration you did (probably through a template in /etc/pmg/templates)
* pmgversion -v
add a queue monitor ( code found here on forum)
add subject to syslog
turn on rsyslog to combine all 3 of our nodes logs so that tracking center shows all 3 nodes.
additionally it seems as if your template does not include the latest changes shipped by us (you can compare your template to /var/lib/pmg/templates/main.cf.in)