Running version 20.8.2432 (build 20.8.5684.561) on Windows 10 Pro 1909.
When I start a Smart Scan, it says Scanning for malware... 0%. It seems to get through the SVC scans and then in the file system it very quickly just stops. The actual file it stops on changes each time I try this, but it is usually something in C:\Windows\System32, but not always.
The Task Manager then shows little activity on the part of Avast.
If I select Stop Scan, whether I follow with Stop Scan or Keep Scanning, it changes nothing. The only way to get past that is to close the Avast window.
On reopening the Avast window, there is a notification that Smart Scan completed and no malware was found. Since from start to hang is only about 12 seconds, I doubt the scan has actually completed.
I updated another PC to the latest version and it will complete a Smart Scan as expected.