Hi guys I have avast updated to 17.7.2314 with the latest definitions. I have windows 10 Fall Update, Before this issue occurred the issue was not present, when ever i run avast boot time scan and it completes which works perfectly to completion. Soon as the pc restarts and I log back into my desktop I can see all my icons and everything as normal but my start icon stops working as I click on it no menus open, it does nothing. If i click on my task-bar icons no icon will open the program again it does nothing. I have to restart my pc again to get my desktop icons working again.
try repair >> https://support.avast.com/en-eu/article/Repair-Antivirus
Why do you run boot scan?
I was testing it, first time i came across this problem i was like huuh, I ran it three times in total 2 without repair and 1 after repair, and it does the same thing. Tested on another pc twice was able to reproduce the issue. If you can reproduce the issue and report it that would be awesome 
If you can reproduce the issue and report it that would be awesomeI dont use avast, but have reported it ;)
Ah ok. Thanks