Typed as I tested stuff, so just a stream of thoughts and observations.
Okay here was a strange observation.
I started Gizmo, it tried to connect to the last MC Server is connected to, my Workstation, and failed.
I switched to trying to connect to my HTPC, which was asleep. As soon as the HTPC started to wake, I cancelled the connection.
I then tried to connect to my Workstation again, and it worked. Just like when I run Pingtools/Bingo SSDP, starting another application allowed Gizmo to connect.
Then I noticed on the HTPC, in the MC "Services & Plug-ins > Media Network" page, that the only record which MC received from my phone, IP Address 192.168.0.11, was a GET...Alive call to a resource on my Public IP Address, and not the internal LAN IP Address. I have port forwarding set up from my Public IP Address to the HTPC, so maybe that is why the HTPC is still connecting?
I turned off Mobile Data on my phone, waited about 25 minutes, and repeated the above process. However, the connection to my HTPC was so fast that I couldn't cancel it. The result was that Gizmo connected to the HTPC. The first record show in MC was again a GET...Alive call, and this time it was to the local IP Address. When I then tried to connect to my Workstation it didn't work.
So I turned Mobile Data back on and tested again.
Alas, the behaviour wasn't repeatable. In fact connecting to the HTPC seems to be faster now. Maybe it is trying the local IP Address first and getting a connection, while in the past it tried the Public IP Address first?
Regardless, Gizmo will connect to the HTPC just fine, but won't connect to my Workstation.
So I tried changing the Workstation MC Server port to 55000. I checked that the JRiver web site had the new port and tried the connection. Gizmo did try to use the new port. Same result though: failed.
I ran Bingo SSDP to see if that would make Gizmo work. Nope. It seems that Bingo SSDP is hardcoded to use port 52199, as the Workstation Library Server didn't show up in it.
EDIT: Nope. The firewall blocked port 55000.So I ran PingTools to see if that still worked. Nope. A scan of the services on my Workstation didn't show up the MC Library Server. I would conclude that the MC Library Server isn't advertising itself, in that case. I may be wrong, but that is what it looks like, and that could possibly explain the whole issue. But then I haven't opened port 55000 in the firewall. Hmmmm...
The HTPC could see the Workstation Server, but couldn't connect to it. Once it failed to connect the HTPC dropped the Workstation from its list of available servers under Playing Now... and added the three DLNA Servers that the Workstation runs to its list. So the HTPC was using cached information which it updated once the connection failed. It looks more like the Workstation isn't advertising its MC Server. But I see SSDP NOTIFY and M-SEARCH transactions from the Workstation both on itself and on the HTPC, even GET calls from my TV to the Workstation, so maybe not.
I changed the Workstation Server port back to 52199. Gizmo still wouldn't connect.
Bingo SSDP then showed the Workstation Library Server again.
Gizmo then connected to the Workstation.
I tried port 52150, which is within the port range I have open on the firewall, for inbound and outbound TCP and UDP packets.
Surprise, that worked. But, Gizmo tried to connect to the HTPC first and I cancelled that. So maybe I was seeing an instance of what occurred above in the third paragraph. So I will have to wait and test again later, once whatever it is has timed out...
... Okay, using port 52150 didn't work either. The Pingtools fix did make it work though. Bingo SSDP also saw the Workstation Library Server as well, so I guess it looks in the port range 52100 to 52200 ( or 52199).
So, querying port 52199 wakes the connection and allows Gizmo to connect.
That is pretty much me done. I don't have any other ideas. Well, I could install Package Sniffer
https://play.google.com/store/apps/details?id=com.packagesniffer.frtparlak on my phone and see what comes through I guess. But a little more direction would be good. What to look for, really?