Jetpack Tiled Galleries use the Photon module to cache each one of your images and create the tiled effect. However, the Photon module won’t be able to cache your images if it can’t download them in less than 10 seconds.
Looking at the images in your gallery, they seem to be extremely large, and take more than 20 seconds to load.
Here is an example: the image is quite large (4068x2592px, 6MB), and I needed 26.33s to load it.
https://i.wpne.ws/bzfm
You can see the problem with your header image as well; it slows down the page so much that it took me 1m17s to load the whole page:
https://cloudup.com/cGcCcPU_LP6
I’m afraid most of your readers won’t wait that long for the page to load.
Try uploading much smaller images; that should solve most of your problems.
I hope this helps.
