I'm having the same issue. Invalid autofill data was entered and when I turn autofill on, my email address will show, but the invalid entry does not. I don't want anything except my email and address info to populate. I would never store passwords or card information, as if you're hacked, the hackers could obtain the info. All the Avast developers would have to do is add a 'Delete' function to the settings.
From what I've seen, Avast is the worst browser developer when it comes to responding to users and they don't have a user friendly method for providing bugs and feedback. Google is pretty much the same from the user comments I've seen. Microsoft has a 'Feedback Forum' and there are loads of items I've seen where the user feedback was taken seriously and bugs were fixed and enhancements added.
I realize they are bombarded by thousands of requests, but if they aren't able to respond to and complete user requests, maybe they need to think about hiring additional Programmers and Web Developers.