I have a brand new Windows 10 Home installation and am encountering the above issue. Avast Free was also very difficult to install (I had to stop the installation twice in Task Manager before it would proceed).
Using the right-click context menu scan individual items option the scan only proceeds a small amount of the time. Otherwise, nothing happens - no error messages.
Avast seems to be causing a raft of other problems, too, especially installation issues. I temporarily switched it off and things started installing normally again.
My father is having similar problems with Avast on all 3 of his Win 10 machines.
I have noticed other, strange behaviour by Avast. E.g. Samsung Magician was not loading and/or not recognising my SSDs. I temporarily disabled Avast, and bang, the program worked at once!
I’ve also had problems installing some progs (though I haven’t made a note of these).
Avast seems to be playing less and less nicely. Combine this with many issues I am experiencing with Comodo Firewall (also needs to be switched off to get some stuff to work), and I am considering taking my “free” custom elsewhere.
Same here, Windows 7 Home Premium x64 / Avast Free 19.6.2383 ~ context scan for single items works normally, but when selecting multiple items the results only show after requesting the scan twice.