I‘m not here to fight with you. You‘re reporting a mixed setup of UPnP and manual port forwarding with accessibility dropping after some time.
The argument „I haven’t changed anything“ is of little value if there’s other players involved, e.g. your ISP (beyond your own statement that you were going back-and-forth with your network settings when attempting to troubleshoot those remote access issues).
I can only recommend you do the basic remote access troubleshooting:
- Disable UPnP
- Establish a port forward, pointing to the machine hosting your Plex Media Server and tell Plex about that manually specified port
- Check if the port is accessible/visible from outside your home network (e.g. using a service like canyouseeme.org)
Yes, there’s always a few users reporting remote access issues. Many claiming it only started after a specific server or client update… in the end the vast majority comes down to some misconfiguration or a backen change by their ISP.
That’s no guarantee Plex won’t get something messed up… but it makes me fairly confident of my feedback.