I have been struggling with this for a while now and finally posted it here: My site runs with Jetpack plugin enabled and I have the gallery's display as Tiled Mosaic. Sadly enough nearly every gallery fails to load all images. There's always some image missing and instead there is an empty space.
I thought this had something to do with my theme using some Lightbox on the images but even when I activate the latest Twentyfourteen theme the problem persists. I re saved every post, it just doesn't help.
When I look in firebug there is an url to the image src element like this:
When I manipulate some of the last digits on that url I finally get the image to show but often in wrong aspect ratio.
Does anyone know an answer to this? It's very annoying!