we have such a problem on magento 2, it started to do this to us when we added more sites, images and products.
It is that when I open our site www.bridgeacademy.cz, go to products https://www.bridgeacademy.cz/cz/krouzky-na-skolach.html , scroll down the page and the images for the products don't show up. However, when I open the site in anonymous mode, they do load. This is a very random phenomenon that also manifests itself in that when I refresh the page halfway through, other (more distant images) do not load. It looks to me as if magento has set some image size that it loads and the rest doesn't load. On phone the images does not load when i am scrolling down, but when i scroll up the images load IDK srsly. I would be glad for any advice. Thank you very much.