YARPP – Only showing on some posts

I am not seeing the related posts on all my blog posts.

Here is a post where they show:
https://www.renefrederiksen.dk/2006/08/20/thomas-edison-museum-fort-myers-florida/

Here is one where they are not:
https://www.renefrederiksen.dk/2011/05/22/benzinoekonomi-teknik-ford-mustang-cabriolet/

Title, tags, description etc. all contain some of the same words in both, so that shouldn’t be the reason.