Sierra 10.12.6 mounting AFP hangs Finder

Since I updated to macOS Sierra 10.12.6, mounting AFP shares hangs the Finder and there is no way to get it stop trying or do anything about it after that other than rebooting the machine. File windows become unresponsive, etc.

This worked in Sierra 10.12.5, but broke with the 10.12.6 update.

Trying to mount an AFP share, the following happens. Here's the click story:

1. Go > Connect to Server
2. I have an entry like afp://servername.mydomain.com, I click on it and select Connect
3. The authentication panel comes up, I select Registered user, enter my name and password*
4. The list of available volumes appears, I select one of the volumes to mount (e.g. Volume_1)
5. A progress window appears saying "Connecting to afp://servername.mydomain.com ..." with a full progress bar (with that light effect running on it from left to right)
6. From here the Finder is unresponsive, you cannot cancel the connection attempt (clicking the X makes a "Stopping" message appear, but it actually never stops.

THIS IS HURTING MY WORKFLOW SO MUCH, I DON'T HAVE A WORD EXPRESSIVE ENOUGH FOR IT. THIS WAS WORKING BEFORE THE UPDATE AND IS STILL WORKING ON MY MACBOOK PRO WHICH I DIDN'T UPDATE YET.