Some images don’t display on mobile devices

Hi,
I noticed that some images of my website just don’t appear on mobile devices, leaving instead a big blank space (no matter how long I wait for it to load or how many times I clear the cache… I have tried on several phones and used different browsers, didn’t change a thing…). On the page I linked to this post it’s the first one, just under the title, that I can’t get to display on my phone, but I have this same problem on a few other pages too, and I’m not quite sure what causes it…
Thanks in advance for your help !

The page I need help with: [log in to see the link]