The URLs are

https://seekreators.org/media/blogs/arduino/quick-uploads/p118/_evocache/gifoptimizirano.gif/fit-1280x720.gif?mtime=1530991309

https://seekreators.org/media/blogs/3d-print/quick-uploads/p172/_evocache/unknown.gif/fit-1280x720.gif?mtime=1538324595

Are you sure the second gif [unknown.gif] is the correct one?

Yes, it is correct that is just the name of a GIF.

As you can see if You open my link when open the first one it will start automatically, but second link You need to click on it to open in Prewire to start

https://seekreators.org/media/blogs/3d-print/quick-uploads/p172/_evocache/unknown.gif/fit-1280x720.gif?mtime=1538324595

I can only think the image in the [_evocache] just isn't stored properly as it does not work alone

whereas https://seekreators.org/media/blogs/3d-print/quick-uploads/p172/unknown.gif does

For now you could change the post image to https://seekreators.org/media/blogs/3d-print/quick-uploads/p172/unknown.gif/