If you have the "Start menu and Cortana" bug, then restart in safe mode with networking, then reboot back to Windows. Fixes the bug for me, but it is definitely due to the presence of Avast. Hopefully the bug get ironed out of the issue in the next update.
I haven't tried this yet. Has anyone else tried it?
I'm not in a mood to uninstall my current av, reboot, install avast, reboot, discover that I still have thd issue, reboot into safe mood with networking, reboot, discover that the issue is still there, uninstall avast, reboot, install the alternative av and reboot again.
Too much of a hassle to try it without at least avast having released a new version.