Las miniaturas del portafolio no se muestran.

<?php
    /*
        Template Name: Página de Portafolio
    */
 ?>

<?php get_header(); ?>


    <section class=fila>
      <div class=small-12 columns text-center>
        <div class=leader>

        <?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

          <h1><?php the_title(); ?></h1>
          <?php the_content(); ?> 

        <?php endwhile; endif; ?>       
        </div>
      </div>
    </section>

    <?php

        $arg = array (
            'post_type' => 'acf_pictures'  
        );
        $query = new WP_Query($args);

    ?>


    <section class=row no-max pad>

        <?php 
            if( $query->have_posts() ) : while ( $query->have_posts()) : $query->the_posts;
        ?>

        <div class=small-6 medium-4 large-3 columns grid-item>
            <a href=<?php the_permalink(); ?>><?php the_post_thumbnail ('large'); ?></a>
        </div>

        <?php endwhile; endif; wp_reset_postdata(); ?>

    </section>




<?php get_footer(); ?>