Have you tried to use the Chrome web browser?
Something is weird in your last screenshot.
The address bar says app.plex.tv, but the message below shouldn’t appear on app.plex.tv. So the content of the address bar and the content of the web page don’t fit together.
Have you granted the web browser the permission to access the local network? I needs this for both app.plex.tv, as well as 192.168.1.37 Important note about the Plex Web app - Local Network Access
