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 already disabled my w3total-cache plugin, re saved every post, it just doesn't help.
Does anyone know an answer to this? It's very annoying!