Ronak,
Thanks for your kind reply.
Fail to see in my single.php file class=”featured-header-image” nor post_thumbnail or get_the_post_thumbnail function

<?php
/**
 * The template for displaying all single posts.
 *
 * @package Lucienne
 */

get_header(); ?>

<div id="primary" class="content-area">
  <main id="main" class="site-main" role="main">
    <?php while ( have_posts() ) : the_post(); ?>
    <?php get_template_part( 'template-parts/content', 'single' ); ?>
    <?php
				// If comments are open or we have at least one comment, load up the comment template.
				if ( comments_open() || get_comments_number() ) :
					comments_template();
				endif;
			?>
    <?php the_post_navigation( array( 'next_text' => __( '<span class="meta-nav">Next Post</span> %title',  'lucienne' ), 'prev_text' => __( '<span class="meta-nav">Previous Post</span> %title',  'lucienne' ) ) ); ?>
    <?php endwhile; // End of the loop. ?>
  </main>
  <!-- #main --> 
</div>
<!-- #primary -->

<?php get_sidebar(); ?>
<?php get_footer(); ?>

Ronak,
Was looking at the single.php file and not the content-single.php file that I failed to see. It was hidden under template parts. Your solution solved my problem. Excellent.
Thank you very much.