Notification is not working for being notified when a new antivirus engine is available. When set to Ask when update is available no notification is given. I can see that a update is available from within the product (Free Avast). This happens on both Windows 10 home and Windows 10 Pro.
Seems to be a common issue. I also have that Bug, been for a while now.
I believe Avast is aware. 
Edit: Sometimes I see a Triangle/Exclamation mark over Avast Icon which leads me to open the UI and see Update is Available…and sometimes I don’t get any notification. :-\
Reported to Avast.