Sydney hero image not showing on mobile

Every now and then, the hero image on some of my sites disappear. It seems it happens after a theme update. I use a child theme of Sydney.

This CSS used to solve the problem but not anymore:

}
	@media only screen and (max-width: 1024px) {
      .sydney-hero-area .header-image {
        background-image: url(XXXX) !important;
        height: 400px !important;
      }
    }

How can I solve the problem permanently?

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