Undernet doesn't support SSL, so if you changed your default port to SSL or the like, that'll explain it.

I connected on the first attempt with the command: /server irc.undernet.org 6667

It connected me to budapest.hu.eu.undernet.org 94.125.182.255 [ircu.atw.hu] (i'm in the U.S.)

You can find a complete list of servers here: https://netsplit.de/servers/?net=undernet

Well. At least I won lunch.
Good philosophy, see good in bad, I like!