Images not showing up in archive or category posts

Here is my blog: https://www.oneeightyone.com/lego/.

All my images display correctly in their original posts. But for some reason, when I click on Archives, or Categories, it will list the posts, with copy if there is any, but not the image from the original post. This is a new theme I installed, previous themes show the images correctly, so I’m thinking there’s some kind of hidden tag I’m missing somewhere in this new theme, but I’m stumped.

Any help is appreciated!