Post and page content not displaying in search results

Question

I am using a content-search.php template part to output my search results. The post/page titles and links to those posts/pages are working correctly, but for some reason the the_content() function is not rendering any HTML. I have tested for errors with debugging on, but nothing is displayed.

Here is my content-search.php template code:

<article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
  <header class="entry-header">
    <?php the_title( sprintf( '<h2 class="entry-title"><a href="%s" rel="bookmark">', esc_url( get_permalink() ) ), '</a></h2>' ); ?>
  </header><!-- .entry-header -->

  <div class="entry-content">
    // No content from posts or pages is displayed using the_content function
    <?php the_content(); ?>
  </div><!-- .entry-content -->

  <footer class="entry-footer">
    <?php flagstaffcounty_entry_footer(); ?>
  </footer><!-- .entry-footer -->
</article><!-- #post-<?php the_ID(); ?> -->

Here is the search.php template code:

get_header(); ?>
<div class="content-and-sidebar">
  <main class="main">
    <?php get_search_form(); ?>
    <?php if ( have_posts() ) : ?>
      <?php while ( have_posts() ) :
        the_post();
        get_template_part( 'template-parts/content', 'search' );
      endwhile;
      the_posts_navigation();
    else :
      get_template_part( 'template-parts/content', 'none' );
    endif;
    ?>
  </main><!-- main -->
  <aside class="sidebar">
    <?php get_sidebar(); ?>
  </aside><!-- aside -->
</div><!-- .content-and-sidebar -->
<?php get_footer();

The the_content function is working on all other templates on my site.

Update

Including offending iframe wrapper filter function for reference.

function themename_iframe_wrapper($content) {
  if( is_page() ) {
    $pattern = '~<iframe.*</iframe>~';
    preg_match_all($pattern, $content, $matches);

    foreach ($matches[0] as $match) {
      $wrappedframe = '<div class="iframe-container">' . $match .   '</div>';
      $content = str_replace($match, $wrappedframe, $content);
    }
    return $content;
  }
}
add_filter('the_content', 'themename_iframe_wrapper');

Any ideas on what I am missing?

Answer 1

The problem in your code is that your function is only returning the content when is_page() is true, which is not on the default search results page, where is_search() is true. Likewise, the content would also not be returned on singular post pages and anywhere where is_page() is not true.

So remember that a filter callback (like your themename_iframe_wrapper() function) must always return the content, just as with shortcode handler functions.

function themename_iframe_wrapper($content) {
  if( is_page() ) {
    ... your code.
    return $content; // don't just return it here
  }

  return $content; // always return the content
}