ASUSTOR remote access on/off

Which means it’s never working.
The Plex remote access status indicator defaults to „green“ while it’s testing your remote access status.

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.