Wordpress网格显示空条目

I've created a grid in wordpress. But sometimes I get empty entries. enter image description here

<div class="row">
    <?php

    if ( have_posts() ) {
        while ( have_posts() ) : the_post();

              ?>

                  <div class="col-md-4">
                    <?php $kale_entry = 'small'; include(locate_template('parts/entry.php')); ?>
                  </div>
                <?php
        endwhile;

    }?>

Do you have any ideas, why is that happening? Many thanks in advance!

set 'min-height:600px' for this div 'col-md-4'. increase the min-height and check.