Everyone seems to think this problem is Virus Checker related, but what they all forget is that they ALL rebooted!
Rebooting always fixes the problem (temporarily). Virus checkers have nothing to do with the freezing up of these two Window 10 features.
I used to be an avid "Avast" user, but now I find that having Avast just adds unnecessary overhead.
"Defender" is fine for virus checking and (being internal to the system) has minimal overhead.
(I still do use SuperAntiSpyware though since I paid for it and it works beautifully under Windows 10...and it is the best for Spyware).
I am investigating an easy fix to the "Start Menu/Cortana Freeze" problem and will get back to you once I find it.