Hello,
the frequency of these popups seems to have increased in case of crashes; and from the content of the popups it seems webshield may be really crashing alot. Please can you check in Console (cmd+space, type console + enter), in the left pane select System Diagnostic Reports, and check for crashes of processes with prefix com.avast. and send them to ondrej.kolacek at avast.com? Also please if you could generate a support package (via menu -> help-> bottom most option -> generate support package) while mentioning your name within? Ideally after the error appears or after a web page stops working correctly? We will try to find out what is wrong.
Kind regards,
Ondrej Kolacek