Hey Edward,
Your posts and some pages don’t have a header because nothing was assigned to them. I checked all your headers and none of them was assigned for the “Entire Site”. To demonstrate that Header Assignment works, I duplicated one of your headers and assigned them to the Single Post Type.
I see your “New Post Header” however, it’s assigned to the About page and not single posts.
Please review your header assignments and their priority. Remember, lower number means higher priority.
If you still have issues, please keep the parent theme activated. Child theme conflict was repeatedly posted here yet it looks like you just tested it lately.
Please note that we do not provide support for the child theme. Fixing custom codes affected by the update is the responsibility of the website owner.
Thanks.