There are a number of things that can break the Windows 10 start menu and Avast IS one of them. I mentioned the Windows XP issue because it’s very similar. The desktop shell stops responding and there’s nothing you can do other than reboot.

And I’m still installing Avast on Windows 10 systems because it only affects a small number of devices which might indicate a conflict with a device driver or something but it does happen.

The Windows 10 start menu/cortana/shell should be more stable and resilient but it doesn’t mean avast isn’t causing a problem.