Following up:
Over the weekend I took @FordGuy61 's advice and went ahead and uninstalled Plex Media Server, following all the instructions for removing library entries, etc.
Reinstalled - no joy. Same deal. Used Safari, Chrome, and Firefox and got the same results. FWIW, I had to circumvent Mac’s Security feature to allow the application to be installed, as it has no developer cert that Apple recognizes.
I uninstalled the VPN client I was using (although it was turned off, it has routing features that may have been left active, and I wanted to be sure it wasn’t blocking content in anyway).
Additionally, disabled DHCP on my ISP modem / router, so that only my mesh router is doling out IP addresses.
Still no love.
Logs attached.
Plex Media Server.log (897.4 KB)