I answer to myself. As often, it was a really simple and stupid detail : when I check post_type in the beginning of my code, I haven’t added my custom post type where I display my ACF WYSIWYG.
My problem is resolved just adding my post type in the following line :
// On vérifie qu'on est sur un article ou une page
if( ! in_array( $typenow, array( 'post', 'page', 'custom_poste_type' ) ) )
