Book navigation pager is moved under the comments
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!