Cannot access home router admin page while web shield is on

I cannot access my home router admin page while the Web Shield (Avast Free 2015) is activated. Getting “The connection was reset” in Firefox and “Your connection is not private” in Chrome. Home router admin page is Tomato USB and uses SSL with a self signed certificate, i.e. accessing it using e.g. https://192.168.1.1 in a browser. Defining exceptions and disabling HNS doesn’t help. The only thing that helps is completely disabling the Web Sheid. (And interestingly enough, when I disable the Web Shield in order to access my router, I can’t enable it again without restarting the computer.)

How to solve this?

Disable https scanning and see if that solves the problem.