That’s the thing, avast doesn’t block links/url, however I’m not sure if the AM Browser is supported by default by avast. You may have to have the opt-in for that program done.
Temporarily have IE or another browser as your default and check if the email hyperlinks work for that.
Sometimes if you have more than one browser, they try to take over the world and be the default browser, almost every time I use one of my 3 browsers it tries to set itself as the default browser.
So if you have more than one browser, they may have had a fight and you lost ;D