Spent hours this morning trying to fix it. I have a unique-ish tunnel setup using Pangolin and a Newt tunnel into my server (running PMS in a Docker container inside a Debian VM in Proxmox). I can reach my https://plex.domain.tld, and so can my friend remotely in a browser. Absolutely cannot be reached externally via apps or https://app.plex.tv. I’ve fiddled with a number of settings and confirmed PMS isn’t detecting any rebinding (used this thread for that).
I’m not sure at this point if it’s Plex’s issue or mine…
