Hero image disappears on mobile devices

On https://jorisvanooijen.nl/cm/ I use the grid lay-out on my front page with a featured image in the hero position. When one looks at the site on tablet or phone this image isn’t shown. How come and how can I get it showing up?
Edit: On the demo, https://edindemo.wordpress.com/page-templates/grid-page/, the image doesn’t disappear So there seems to be something wrong with my child-theme?

• This topic was modified 6 years, 1 month ago by tastymouse.