Files in page folders gets excluded from navigation

[ahku]

For some reason this works:

/pages
  /folder
    index$.md

But as soon as you add another file, the whole folder and its contents disappears from the navigation:

/pages
  /folder
    index$.md
    another$.md

You can still access the page via /folder/another, but according to the documentation there should be support for nested pages.

Is this an issue with the theme or the actual plugin?