Masonry grey/missing thumbnails

I am trying to use Masonry, but some of the thumbnails are missing or greyed-out.

It bugs my because I have another site where this is working fine and looking really good, but I can’t figure out the difference.

The overlay panel works fine, so I don’t think this is access issue to Smugmug. I also tried local media, and it has the same issue.

Thanks,

Ron

The page I need help with: [log in to see the link]