Thx for your indications. It works well!
Is it possible to add in Custom Post Navigation hook elements, a section with related posts (without a new plugin).
Btw, the space was an adsense code. Founded & delated.
You will need to install a Related Posts plugin.
Most of them provide a shortcode or PHP Function for displaying the posts.
You can add that code to the Hook Element to display them in the same position.