Missing primary navigation on a specialized page

The site: https://www.devil-music.com/

The custom page missing the site navigation: https://www.devil-music.com/travelling-books/

All pages and page templates {general, custom, and specialized} call:
get_header();
No pages have a “parent” set and all have an “order” of 0.

However, somehow the problematic page gets no navigation populated, resulting in:
<div class="nav-menu"></div>

The primary navigation shows up on all other pages.
– Home page (also specialized using a page-{slug}.php template): https://www.devil-music.com/
– About page (also a page which isn’t the home page but is included in the navigation): https://www.devil-music.com/about/
– The landing pages (also pages, purposely not included in the navigation), eg: https://www.devil-music.com/buy-the-book/

I am using a custom child theme of Twenty-Fourteen. The site is hosted on AWS.