It seems like the plugin can't handle private posts. For testing purposes and to adapt my style.css I created a couple of private posts and added them to a article serie.
- The serie is shown correctly when editing the post
- The serie is shown correctly when listing posts
- I can filter the posts with the serie
- When I list the series the serie shows 0 posts (even though there are 4)
- Displaying a post the plugin shows "Part X of 0 in serie ..."
- The box containing all posts within the serie is empty
- The Series Meta is not showing
I tested the same setup on another WP instance, as soon as I set a post where the plugin worked before to private, it half vanishes from the serie.