Main Site Thumbnails broken

[Kemelvor]

Hello,
I have a troubling problem and i'm pretty new on this website.
I uploaded 4 gifs, the first one was fine. The 3 others have a broken thumbnail/Image preview. No matter what i do, i cannot make them functionnal.
I tried deleting those image and reuploading them.
I tried assigning them a custom 600 x 600px thumbnail, in png, jpg, gif.

http://imgur.com/IHMtD4g

Still have broken thumbnails. Is anyone know what is causing this ?
Thanks

 

[Kemelvor]

Because i have found the (temporary) solution by myself and no research gave me the answer, I will give this for the next one who will encounter this problem :
Limit your gif size by 450x450px max and it'll work. However you still cannot use a custom thumbnail.

 

[Fallowfox]

Well done on figuring this out, it's useful for other users.