The original is too big...avatars have a 75x75 limit, while that one is 80x80. The forum software can automatically shrink avatars when you upload one that is too big, but I assume it can't do that for animated ones and just grabs the first frame and shrinks that.
You'll have to manually shrink the original to 75x75 pixels (the file size is already fine, so no problems there) and then upload it.