Attach to Unity not working with Visual Studio Professional 2017

I have been using VS Pro 2017 for 2 years straight on Windows 10 with the same computer, and all of a sudden the Attach to Unity is not working.

VS Pro shows the orange bar at the very bottom when I click the Attach to Unity button, but then switches back to blue and shows this in the log:

Code (CSharp):

1. The program 'Unity' has exited with code 1 (0x1).

after loading all the modules.

This happened once before, a month ago, and I resolved it by uninstalling VS Pro 2017 and reinstalling it. I just tried that again, but it did not work this time.

Anyone have experience with this, or have any ideas?

 

I have tried:
1. uninstalling and reinstalling VS Pro 2017
2. modifying VS Pro 2017 to remove and then re-add the "Game development with Unity" package
3. starting Unity as an admin
4. changing the editor in Unity Preferences to something else, then back to VS Pro 2017