Featured image not showing up

Hi, I created a child theme for Vega and for some strange reason, the featured images aren’t showing up on the default template when they’re added. It’s just a grey box without an image.

Is Vega different to where I need something special in my child theme’s functions file for this to work? I can’t link to this because our dev environment is hidden behind firewalls but I’m happy to share screen shots via email.

The page I need help with: [log in to see the link]