Briefly, I switched to a new ISP. Now my server shows as unavailable when I log into Plex-web. Plex itself is running on a Synology NAS. Everything works ok on my internal network, and I can get to Plex account settings when launched from the NAS itself. But not from a web browser.
Did you turn off remote access and turn it back on again with your new IP address? That’s all I had to do when I switched ISP’s. If that doesn’t work, go to canyouseeme.org and see if it shows port 32400 (or whatever port you have open,) as available to the internet.