Static page does not identify a template

I have two pages, one works fine and one is broken.

The first is named Calendar and has an ID of 34. I've created a page template called page-34.php and written custom code. When I load the page, the template is retrieved correctly and the custom code is displayed correctly. I have a bunch of other pages on my site, and they work that way.

And then I have the second, lively side. The name is FAQ and has an ID of 35. I have created a template called page-35.php and written custom code, but when I load the page I use index.php by default.

To provide some background information, I recently imported all the content from a Drupal 7 site with a plugin. I wonder if something went down during this process. I'm a pretty experienced WordPress developer and have done all my usual checks on this problem. So I am at the point where I want to do a deeper debugging.

Question: Does anyone know how to do a deep programmatic debugging of the template hierarchy? I am not afraid to get my hands dirty in the database.