I am having a problem where using certain images as the featured image will cause a post not to render if said image is enabled to appear at the top of the post. With certain images, the post will not render and will only show a grey box. With others, the post will render correctly. This situation does not seem to be a size problem since some larger images (6MB) work and some smaller images (2MB) do not. Any ideas what could be causing this problem? Thanks.