The only avatars that are working are those stored off the avast forum, all the links are there for the internal forum avatars (image1), but you get a 404 error if you try to display them (image2). External avatars aren't effected.
Notice in image1 that the URL starts off https: and this is what I believe is the cause of the problem. If I drop the 's' down to http then the link works and displays my avatar, image3.