Note added later: when I changed the router to route FTP differently, I forgot to tell the "2111" server that I'd done that, so it was receiving port 21 from the router, but vsftpd.conf was listening for port 2111. I changed it back. (Will have to do that to the other server since the router now routes port 2111 for FTP to that one instead). SEE BELOW FOR SOME TRICKS AND INFO ABOUT THIS ISSUE.
Suddenly, PHPStorm's update via FTP stopped working. Maddening. I still cannot account for why. Sometimes, you just have to fix it however you can and get on with your life.