The Web UI controlling remote access is badly written. The text indicating success vs. failure flickers and often lies about the state of connectivity. Please improve both the default result text, and ensure that ONLY the correct result displays.
The difficulty of remote access setup should be limited to configuring NAT, not having to work around Plex Web UI glitches!
The UI is correct at the time it checked the connection. If the information is wrong, your browser may have cached the page and providing the wrong info. Or something changed since the last check. Your server isn’t doing a continuous check, that would be a waste. It only checks when you change something, then periodically every couple of hours.