For the last few weeks and more so just a few days ago Plex remote access has been dropping and becoming unavailable. Port 32400 has been forwarded, VPN has been turned off, Secure connections, firewalls has been disabled to test. This issue seems to be with Plex install itself. I have had Plex for several years and this is the first time it’s done this.
Have you verified the published port is accessible from outside your network?
If it isn’t… have you tried using a different port for your port forward?
When you say it’s becoming unavailable… are you referring to the Remote Access status indicator within Plex or have you experienced remote clients not being able to play things back?