From what I can gather, the old forum version had Profile Pictures and Avatars and you could set different pictures for each. The new version appears to only support profile pictures. (Thanks to Elw3 for pointing me in this direction). I would ask users with malfunctioning avatars to try setting their profile picture explicitly. You can right click the existing picture to get the link to it and try using that for your picture in your profile. I see no way to restore the old Picture/Avatar split.