Header image no longer displays

I had an image in the header, but is was 1920×1280 and of course was cropped. Today I added a new image with the recommended 1600×800 dimensions, and in the customizer it shows the thumbnail of the selected image, however in the preview, or when I view the site all I have is a black page with my hero section title & subtitle. The image won’t display. I went back to the old image but it still won’t display. Any advice on how to fix it?