Wow, this worked for me!
I used the KB article on changing an IP of a server...
and obviously it's meant for a new out of the box default, whereas my server was already upgraded,
but the article (probably correctly?) did not mention this server.xml file for the webproxy
and once I made this change, editting that file to change old IP to new IP, restarted everything, works great.
Definitely, if you have this problem, check that file.