Hi,
The problem is that the plugin only sets $poi->postid for mashups. For individual maps you’ll need to take the current post ID from the global $post.
I’d like to to get this fixed, since it’s inconsistent – but until then you can use something like this:
<?php global $post; ?>
<?php $postid = ($poi->postid) ? $poi->postid : $post->ID; ?>
<div><?php echo get_the_post_thumbnail($postid); ?></div>
<strong>Grid Reference:</strong> <?php echo get_post_meta($postid, 'wpcf-grid_reference', true); ?><br>
<strong>Recorder's Name:</strong> <?php echo get_post_meta($postid, 'recorder_name', true); ?><br>
<strong>Sighting Date:</strong> <?php echo get_post_meta($postid, 'sighting_date', true); ?><br>