Hello,
the issue is somewhere in our code that does an analysis of disk configuration. Due to this taking excessive time, the scan fails to even start. For two our users, this has been caused by an external drive being plugged in when scan starts. A workaround is to unplug an external drive before starting the scan.
This is indeed a huge issue, although this does not impact fileshield, so it should not be a security issue regarding viruses on your computer; however not being able to scan is indeed somewhat unfortunate

Please if this happens for you and you've got few minutes, consider helping us by following these directions:
1) plug in the disk that causes this
2) run scan
3) run Activity Monitor app (by eg pressing cmd+space and searching for Activity Monitor)
4) Go to menu, View-> All processes
5) find process com.avast.scan_helper in the list, double click it
6) on the bottom left is a button “sample”, press it and enter your password
7) use “save” on the top right to save the sample

ideally create 2-3 samples, but even one is better than nothing

9) send it to ondrej.kolacek at avast.com
10) send us support package (
https://support.avast.com/en-ww/article/Submit-Mac-Security-support-file) and specify the same mail used in 9) so that we can match these.
Hopefully with this information we will be able to verify that we have indeed found the issue and will be able to ship an update ASAP.
Kind regards,
Ondrej Kolacek