I've been struggling with this for the past hour, and finally got it to work.For me the problem seems to boil down to the displaying of tiles themselves, not the images, not the cdn.
Here's what I've been experiencing.
I've been getting blank spaces where images are supposed to sit. In a gallery of 10 images, one is missing. When I removed the image from the gallery, the next image took its place and disappeared. I added it back, and switched the image's position in the gallery order. Got nothing. Re-create the gallery? Didn't work. Re-named the image in media editor and tried weeeweeeweee's suggestion of "rotate, save, rotate back, save" to no avail.
I tried re-arranging the images in the gallery one more time.
I feel it's also worth mentioning that Photon has never been activated on this particular WP installation.
Here's a link to the page. I'll leave both galleries (the corrected one, and the broken one) up for the next day or so in case anyone wants to take a look.
UPDATE: It does seem to be a display issue. This may differ from Mvd's problem, but I hope it is useful.
I inspected the html of the "gallery-row" div, the one that contained the missing image. Its width is 671px. Inside it, there's two "gallery-group images-1" divs with widths of 436px and 236px. combined, that makes 672px.
The second div was getting bumped down to the next row, and was hidden behind the next image in the sequence. I changed the 436px width to 435px, and the image popped back into place.