Featured Image Not Showing in "The Next" Theme

I changed my theme to ‘The Next’. Initially the featured images showed, but after I started changing the options in the Customize dashboard, my featured images disappeared. I see them in the post editor, and I tried reuploading some of the images to see if that helped, it didn’t. Other pictures show.

I can’t seem to find any option that indicates that it would have an effect on the featured image.

Please help.