Avast blocks valid web sites

Windows 10 Pro with most current Microsoft maintenance. Dell Inspiron 17 7746 laptop.

I have been running Avast Free for several months with no problems.
Today I am at a resort that has a Brighthouse (now Spectrum) proxy server that requires a password to access the Internet.
I connected to Internet via WiFi at the resort and most valid web sites will not load.

Oddly, google.com and facebook.com pages work correctly.
All other sites get the header that changes the browser tab description, but then go into a waiting to load state.

I discovered that if I disable the Avast web scanning function all web sites instantly start working properly.

Could someone please explain what is causing this bad behavior?
And how to correct it?

Thanks,
Terry