i have a similar problem just using a OpenVIX Sat reciever with a HD homerun plugin. It has worked for the past few years, but with one of the server updates in middle of february it stopped working, and Now I cant add my HD homerun DVR.
I can see from the same computer the HD Homerun service so I do know the homerun box is available on the network
I do hope you have an idea, or a new plex update comes out to solve the issue?
Is the server Mikkel-Plex ? Is it on same subnet as the HD Homerun?
In your screenshot it looks that you put in IP Address 12.168.50.129 and not 192.168.50.129 - if SSDP is not disabled could and the HD Homerun is on the same subnet then you do not need to enter the IP manually and the networked DVR should be discovered automatically
If manually specifying the IP Address - do that without the port number and make sure it is the right IP address
If you still have problems please make sure server runs with debug logging and restart the server to get fresh logs then capture the logs and screenshots - do the test with automatic SSDP discovery and then later on with manually specifying the IP address - please do the tests with the SiliconDust HD Homerun and let me know which model
sorted it out by an update on my HD box and Plex Server update.
I needed to clean out the Plex database and then I could remap the HD Homerun.
I do have problems that the EPG guide continue to be lost for some reason?
it is updating but the guide is not loaded, has been working just fine.
I can;t really look into issues on your server whilst you have Plex Media Server binary running in two different instances - one as a service or scheduled task and one as a normal logged in user session
If you run it as a service you must not have auto launch on login for the user account that installed Plex Media Server