Book navigation pager is moved under the comments For some reason, if I change the display order of any field in Manage display for the Article content type, the Book navigation pager is moved to the far bottom under the comments.


  


If I check the template output, it is showing under the comments, which was not the case when everything was right. Even reordering the fields in Manage display to where they were before fixes this. 


  


Is there any reason for what happens? Is it a bug?

I am using the Bootstrap theme, if this makes any difference.
This sounds like a weight issue. 

First: Try actually setting the field display weights.

1) Click the "Show row weights" button.


2) This will replace the drag and drop interface with an integer weight field. Set the weights to be lower (more negative) for all of your field items. Hopefully, this will allow them to float above the comments field.

Second: If the above doesn't work, then you might have to manually set the weight of the elements by altering the form.

You will need to place your code in a custom module. And then using hook_ENTITY_TYPE_view() alter the weight of the comments form.

Your code would look something like this: 

// This part would go at the top of your mymodule.module file.    
use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Entity\Display\EntityViewDisplayInterface;


This is where you actually set the  weight of the comment form.

function mymodule_node_view(&amp;$build, EntityInterface $entity, EntityViewDisplayInterface $display, $view_mode) {

  // This probably isn't exactly what it will look like for you, but it's close-ish.
  if ($entity-&gt;getType() == 'book' &amp;&amp; $view_mode == 'full') {
    // Not exact, but this should be pretty close as well.
    $build['comments']['#weight'] = 30;
  }
}


Hope this helps!