Featured images not displaying with Apostrophe Theme

Hi!
I am currently working on this website: https://visualnarration.wordpress.com/
My theme is Apostrophe.

I uploaded featured images for each post that I created and selected “image” in the post format options. However, when I look into my categories (my posts are organized by categories, they’re not listed on the home page) I can’t see the feature images, I only see a gray square with an icon of the format of the post (a camera).

I would like my featured images to be displayed rather than an icon, and I can’t figure out why this is not working.

Thanks for your help!

Sarah