3D FlipBook - Pdf shows grey squares instead of pictures

We use the 3d flipbook pro and on a lot of devices we see grey squares where images should be. On some devices it's working 100% and other devices we are missing 2/3 of the images. What can be the problem? See: https://villavendee22.nl/magazine/

On mobile almost all photos are working. (i only see 1 picture thats not working)