My apologies guys, I had to go away for 2 days. Will be back today and grab necesary files, and have to say really appreciate your willingness to help!
As a precursor, before I left, I used NMap to try UDP port scan from both different subnets/network segments (zones) and same subnets/segment. Both came back as open|filtered.
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Allright, since clients are remote I could not run Wireshark, but I tried my best to get outgoing and incoming debug. Attached the files to this post. Server IP is 192.168.2.37.