Page attribute box not working after custom theme update

Hello,
I am working to bring an outdated site up to speed, it’s built using a custom theme from an HTML boilerplate.

I have the site on a staging server and when I updated it everything seemed to be working a few days ago. However, there are 6 pages that all use the same custom post type layout that now are defaulting to showing the “archive.php” template.

Furthermore, in the admin section, when I go to one of these pages, the “page attributes” box is not visible. It is checked as “visible” in the screen options menu at the top of the page, but not visible on the page in the sidebar. If I uncheck “page attributes” and then check it again, it shows up and shows that this page is using the correct template from the dropdown list. So I click update and check the page on the front end, it’s still using archive.php and in the admin section, after the page save, the “page attributes” box has disappeared again.

Any thoughts?