Wierd. Are you using the right template version for the MyBB version? The issue is because <!-- start: postbit_avatar --> is duplicating the <!-- start: postbit_author_user --> profile picture. In myBB tempates, look for <!-- start: postbit_avatar -->. You'll have to look up which template to edit, I can't remember off the top of my head. Just delete the image link under <!-- start: postbit_avatar -->. Oh and backup your templates first