there is a bug in 9.5.2 for static routes so if you use this verion you should upgrade to 9.6.0 MR4 in this version this issue is fixed.
to trubbleshout this problem you need to go with ssh on the ESM and make a TCPdump on eth0 i think. You can filter by your destination IP that should get the forwarded Events.
need to understand the steps of forwarding events from SIEM and its uses.
We are at the latest release. I am working with support to resolve this but they still have not fixed it.