Thank you very much! The problem was the subscription, you have to pay for certain things like going through https: domains!

Thanks for responding. I tried to filter out what's happening. The only apparent difference between the single images and those that are displaying double (and even triple) is when I use the same image url for more than 1 listing. So if I have 2 listings with an image url pointing to the same address (I use Cloudinary), the first listing will have two of the same images stack up like the screenshot above, and the second listing will have 1 of the images displayed..It's a strange behaviour but I have absolutely no idea how to fix it. Do you have any idea what I could be doing wrong?