Plex PS4 App unable to connect to local server, AND the UI is completely unresponsive



I'm running the latest server (1.7.5) on a MBP, and trying to access the server via the latest PS4 app (my PS4 is up-to-date with system updates). I am able to run the server, get the 4-character code, "link" it to my account, but then the PS4 app says " is offline or unreachable. We tried to connect to ...".

However the UI is utterly unresponsive. There are three buttons down the bottom - "Retry", "Home" and "Settings". None of the buttons on my PS4 controller (yes, it is working normally) move the active button. It is completely unresponsive. I stared at it for a while and suddenly it moved two boxes to the right, but I wasn't able to select the "Settings" box, and by the time I looked again a "screensaver" (perhaps?) had started, blocking the screen. Nothing I did on the PS4 controller removed it so I'm now stuck looking at a "Plex" logo on a black screen.

I've tried restarting the app several times, and re-linking twice. The server is working fine from the same computer it's running on.

I don't have any fancy firewalls or routers - just a wired switch between the PS4 and the server.

How can I enable insecure connections on the local network if the UI won't let me interact with the App?