I am pretty new to McAfee's ESM, our installation is only a few weeks old and we had the same problem.
I fixed it by doing what is mentioned on page 283 of the 9.3.0 product guide.
You have to define a parent source as your Syslog server with its IP address (so the receiver's firewall permits incoming packets from this IP) and choose "Syslog-ng" in the "Syslog Relay:" section of the source's properties,
Then you define additional data sources with the IP address of the original device that sends its logs to your syslog server.
The kind of data source (parent, client, child) for these additional sources is not mentioned in the documentation; I used client data sources and all my devices appear indented under the syslog data source in a folder called "Group 1". I didn't find a way to rename this folder; it's not elegant but it works. Now all my sources appear as seperate sources.
Universitéd de Sherbrooke
With syslog-ng , the first all datasource is same IP but McAfee SIEM have auto learn
, when you turn on auto learn , about time McAfee SIEM have detect , log is of one of vendor and allow creat datasource at windows auto learn. If Auto learn not know vendor, you can see log and choose vendor. If you dont know vendor , you can parser rule.