I don’t like coding in CodePen so I used WebStorm IDE when I did my tribute page.
My problem comes when I view my page in mobile (via Chrome’s DevTools).
When I view my CodePen page from a simulated Nexus 5X, I don’t see the images in the well at the left column anymore. But when I view the version from my WebStorm IDE, the images are okay.
This looks like a weird quirk that only affects Codepen and Chrome inspector…I haven’t come across it before, but I get the same problem as you running your pen.