Hello Miklos-
Thanks for the great question, and thanks for using W3 Total Cache.
It’s tough to say for sure, since it looks like you’ve disabled W3 Total Cache right now, but I believe the issue might be caused by the fact that both W3TC and your theme are trying to lazy-load the images.
If you inspect the images, you’ll see a class from your theme, zeen-lazy-loaded
, that implies the theme itself is doing some lazy-loading work. If you re-enable W3 Total Cache, make sure that you have Lazy Loading disabled in your Performance > General Settings > User Experience section.