In that case it doesn’t seem to be an issue of your Plexamp app (or the device it‘s running on.
I suspect you might be seeing a „green“ remote access status indicator while Plex is testing the connection. This test usually only takes a few seconds… under certain conditions it might also take several minutes.
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.
