Transient fragments don't seem to work

I am trying to implement transient fragments, I've been doing what is suggested here: http://ift.tt/14uGgEO

Here is my code, in functions.php

function fragment_cache($key, $ttl, $function) {
  // getting a custom cache optin value, randomly generated in backend when a user hits "flush cache" button
  $cache_version = get_option( 'clear_cache' );
  if ( is_user_logged_in() ) {
    call_user_func($function);
    return;
  }
  $key = apply_filters('fragment_cache_prefix', 'fragment_cache_').$key.$cache_version;
  $output = get_transient($key);
  if ( empty($output) ) {
    ob_start();
    call_user_func($function);
    $output = ob_get_clean();
    set_transient($key, $output, $ttl);
  }
  echo $output;
}

And here is my code in my page

<?php while ( have_posts() ) : the_post(); ?>
    <?php 
        fragment_cache('post' . $post->ID, DAY_IN_SECONDS, function() {
            include( locate_template( 'partials/related_article.php' ) );
        });
    ?>
<?php endwhile; ?>

where in the include I am just posting a title and an image

My issue is that the code doesn't throw errors, but if I change my article title, I see the new title instead of the cached version. Any idea?