The slug in question is boats.
By blank page I mean all theme parts load, just the content area is completely empty.
I have worked around the issue by not using a custom post type for boats, instead simply rewriting the child post types’ URL to be boats/child
Now my issue is that all ‘new boats’ (a child post type) URLs do not resolve to a page, giving a ‘Nothing Found’ page.

And the page for this new boat:
