I'm also getting the same cloudfront URL (hXXps://d3ag4hukkh62yn.cloudfront.net) warning when accessing a link on Amazon.com. It's inconsistent (sometimes I can get through, sometimes Amazon is blocked by Avast), but it happens most frequently when I'm on the page hXXps://wXw.amazon.com/gp/css/homepage.html and then hover the cursor over the "Hello (Username)" near the upper right corner of the page (to the left of the "Returns & Orders" link and to the right of the language flag icon). For me, this just started this evening (June 20th) US time. I had accessed the same page and links without a warning today late in the afternoon. I've already submitted a suspected false positive report and hopefully others will do so too.
FYI, you can get the warning every time by entering the above-mentioned cloudfront URL directly. Also, if you type in the URL into a Google search window, there are several hits for this identical URL going back at least a couple of years (one from a MalwareBytes forum from Feb 9, 2020). Also if you enter the cloudfront URL into VirusTotal.com, it reports it as being clean (previous to my uploading, the same URL was posted yesterday on VirusTotal). Interestingly (to me at least), Avast is not listed among the various engines evaluating the URL.
As others have noted, this does not seem to be browser-specific (I get Avast warnings for this URL from every browser I've tried).
Update: Entering the cloudfront URL from Tor does NOT generate an Avast warning - instead it takes me to what looks like the Amazon.com homepage (though the URL in the address bar still says cloudfront). To quote Alice: "Curiouser and curiouser"