One workstation gets slow access to the server, but others are fast
Solution 1:
I've determined the cause of the problem. In my testing, I've been using the server's machine name, PITA2. When I tried using it's IP4 address (192.168.0.100), connections were fast again.
On my older machines I would usually add the server's name+address pair to the file c:\windows\system32\drivers\etc\hosts. Windows has become better at resolving network machine names, so I had never done that on my new workstation. When I changed the server's Network Discovery settings, I suspect that the name recognition facility was hamstrung somehow. It still figures it out eventually, but it takes a long while.
The rest of the machines are older, and still have this explicit entry in their hosts files, which is why they don't have the connection delay.
Now I need to figure out what changed on the server, so that I can change it back.