Remote access suddenly won't stay connected

Consider it’s not working to begin with. Plex takes an optimistic approach, displaying the remote access status as green while it’s still testing the connection.

Did you already have a look at the related troubleshooting support article?

https://support.plex.tv/articles/200931138-troubleshooting-remote-access/

There’s also a guide with some more details on how to troubleshoot remote access issues: