Hello!
From the description you gave it is hard to find out what is happening without some more information.
Can you share your configuration, please?
Do you use the internal source, wildcard file-source?
We also have a tool that can be used to collect environment and information called 'syslog-ng-debun'.
It can collect sensitive data, so be sure to replace/remove those before sending the debun, e.g. IP addresses and passwords from config, etc.
As you are using Solaris as syslog-ng 3.12.1 have you built it from source or used a package?
Best Regards,
Gabor