Instagram images not showing, but posts are clickable

As described in my title: The instagram feed on the website doesn’t show the thumbnail images, but once you hover over the space where the images should be, the link to the related insta post is working.
I’m not sure how long the error already exists. Just noticed it by accident. But I remember everything worked fine after my last system update a few weeks ago.

Same problem on other customers’ websites where Social Slider plugin is used.

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