External Connectivity Broken by Update

Why is it plex says “Your server is signed in to Plex, but is not reachable from outside your network.” when I can connect to http://my-ip-address:32400/web/ just fine from anywhere remotely? This problem cropped up after I upgraded the server, and I can’t figure out what’s wrong. I can connect to the system via the web, log in via remote desktop, ping it, etc, but plex won’t agree that it’s visible!
[-bash-4.1]# telnet my_hostname 32400
Trying my_ip…
Connected to my_hostname
Escape character is ‘^]’.
^]
telnet> quit
Connection closed.

HELP!

Bump - help!