Search displays only 1 result.

Hi,1. I have put a search on my wordpress, but it seems to display only 1 result everytime and I don’t know why

<h1><?php printf( __( 'Search Results for: %s' ), '' . get_search_query() . '' ); ?></h1>
<?php if ( have_posts() ) : ?>
  <?php while (have_posts()) : the_post(); ?>
   <a href="<?php the_permalink() ?>" rel="bookmark"><div class="boxy">
 <img src="<?php video_thumbnail(); ?>" width="378px" height="220px;"   />

      <h3><?php echo get_the_title(); ?> </h3>
<h5 class="artistindex"><?php
  $posttags = get_the_tags();
  if ($posttags) {
    foreach($posttags as $tag) {
      echo $tag->name . ' ';
    }
  }
?></h5>

  </div> </a>
  <?php endwhile; ?>
<?php else: ?>
  <h2>Nothing Found</h2>
  <p>
    Sorry, but nothing matched your search criteria. Please try again with some different keywords.
  </p>
<?php endif; ?>

<?php if ( $wp_query->max_num_pages > 5 ) : ?>
  <div class="prev">
    <?php previous_posts_link( __( 'Prev' ) ); ?>
  </div>
  <div class="next">
    <?php next_posts_link( __( 'Next' ) ); ?>
  </div>
<?php endif; ?>

https://guillaume-loreau.fr/project/?s=swoon

Thanks a lot for your time.