If you have setup a port forward of a public port to local port 32400 for the local IP of the server, you need to ensure that you have ticked the Manually Specify Port box on the Remote Access Advanced server settings and entered the public port that you forwarded in the box
You also need to ensure the local IP of the server is DHCP Reserved in the router or is static and outside DHCP range
If that is all correct, then please make sure you run with debug logging enabled
See https://support.plex.tv/articles/201643703-reporting-issues-with-plex-media-server/
Restart the server to get fresh logs created
When the issue arises, open up the remote access settings page with show advanced. Refresh the page with F5 browser refresh and take a screenshot and download the logs and attach all here
See https://support.plex.tv/articles/200250417-plex-media-server-log-files/
