Hello,
thanks for the web pages; it seems it is working correctly for us. Please
1) send us support package as described above; from that we can see stuff like version of OS, version of Avast etc.
2) the pages that DO work: are they pages with EV certificate? EG. in chrome in the bar with url, instead of icon of lock with text "Secure", ev certifikates have there a lock and a name of a company instead
3) in Chrome, when you get the error message "your connection is not private". click on the "Not secure" up there in the browsing bar, select Certificates
or in Safari, click on Show Details, send us the details text (eg. ondrej.kolacek@avast.com), if there is a link "view the certificate", click on it, expand details, print screen and send us the picture.
This should give us enough info to find out what is wrong.
You may also just try to reinstall Avast, maybe it will fix the issue.
Kind regards,
Ondrej Kolacek