Primary Menu disappears on pages with header created through custom layout

Astra Pro user here. Primary menu showing correctly on website, but disappears when I create a new header through custom layouts.

If I choose to display the new header on only single posts, it will not show the primary menu on these pages but the rest of the site is fine, so it’s clearly something I’ve missed somewhere in the custom layouts. I’ve activated and deactivated things a number of ways but I must be missing something.

Thanks in advance.

I don’t have a site to share as it is in a private testing space.