I have tried adding this image to the page from both the gallery and the media library. I have tried deleting the image and adding again. In all cases the image shows in preview, but not when the page is updated. It doesn't show up in the code either.
I thought this might have something to do with it being a sub-page, but I have repeated this with another page that already has an image and have found that additional images don't show either, including duplicates of ones already on the page.
I have a development site subdomain for this website as well. I tried the same thing and when I updated the page the image showed up immediately. I am stumped.