I tried to update VS to the latest version and encountered a looping error in the Telerik Xamarin extensions.
After killing VS, I was able to update but the UI would then hang as soon as I tried to right-click on the project tree view (if I waited long enough - 45-60 seconds - it would sometimes "come back to life" but would still be unworkable).
Disabling the extensions did not fix the issue. I had to repair VS and reboot.