Just to add, some i.stack.imgur links are apparently badly autofixed or point at the wrong thing. You'll need to change them to i.imgur links.
Here's an example where we needed to do it.
Essentially whatever script changed http://i.imgur.com/ to the new host assumed that the images would have the same filename - in these cases one was empty, and one didn't belong. Changing the links back to i.imgur should give you the original images. Then reupload them to get the correct image on i.stack.imgur and you should be good.