I’ll take another look, but I didn’t see any such setting when I was trying to diagnose. And I haven’t changed any Plex settings since the last time we had an internet outage and it worked properly, just a month or two ago.

I recently discovered that Plex no longer works over local network, if you lose internet service. A) you can’t login without internet access. B) even if you’re already logged in, apps do not find and recognize your local server without internet access. So, yeah, Plex is already there.