Firewall Rule - Plex Media Server - Accessing HD Homerun on Different Subnet

[EricPerl]

He explained how pure discovery failing is expected (the help mentioned is a broadcast relay).
Once you enter the IP, he seems at a loss to explain why (it worked in his test).

The live view screenshot shows out traffic only (all destined to Plex), possibly from streaming clients.

As you press that connect button on Plex, you should see in traffic on that interface (source being Plex).
Per Plex thread, standard HTTP.
Share your rules on that interface. Maybe you don't have logging enabled.