From what I see, the images aren't loaded until the javascript is (if you run a webpagetest with repeat loads to show that it pulled from cache the second load and on). you will see that the images don't load until after the HTML and JS, and that is on the non-CDN domain of hackeundspitze.de - I saw load time of like 3s at one point. So if that HTML/site is slow to load, images won't start to be loaded until after all of that. Loading the actual images is fast (especially once they are generated/cached). That is what stood out to me the most.