syslog sending to syslog-ng

Systems upgraded to OES2 are running syslog. Sending to a new server which installed with syslog-ng.

While I got this going and could, via command line, send message to the syslog-ng server, not all expected messages are arriving. I can see them in the sending server's logs, but not in the syslog-ng server.

Which server's messages get lost seem to vary.

Ideas?