Get Current User Id Inside a Loop Returns 0 For a Shortcode

You have added get_current_user_id(); in single quote. please remove quote from 'get_current_user_id()';.

function get_meta_value_by_meta_key(){

   $author_id = get_current_user_id();
   // do stuff to get user I
   $author_posts = get_posts( array('author' => $author_id, 'numberposts' => -1 )); 
    // needed to collect the total sum of views
   $counter = 0; 
   // needed to collect the total sum of views 
   echo '<h3>Post views by Author:</h3><ul>'; 
    // do stuff to get author name
    foreach ( $author_posts as $post ) { 
       $views = absint( get_post_meta( $post->ID, 'Creation_Views', true ) ); 
       $counter += $views; 
       echo "<li>{$post->post_title} ({$views})</li>"; 
    } 
    echo "</ul><hr /><p>Total Number of views: <strong>{$counter}</strong></p>";
 }
 add_shortcode('Stats', 'get_meta_value_by_meta_key');