Just installed Avast Premium on my Windows 10 Pro Laptop and started to have this issue.
Previously I was using Avast Free without a problem.
The problem I am having is only in MS Edge and not in Chrome.
When I go most of my financial sites (bank, credit card, etc) the site does not load and I get a message “Your connection is not private. Attackers may be trying to steal your information” net:err_cert_invalid.
I also can get the error on part of a site, so I can go t bloomingdales.com, but if I try to pay my monthly bill I get the error.
The site could be a bookmarked or cached site or a totally new site I have never been to before.
Not using Avast Firewall.
If I disable Core Shields the problem goes away.