Not exporting featured images that aren't posts attachments

#FILE: dms3-export.php

1. remove/comment out that debug line after XML header:
echo 'post_ids';

2. When not using full export – currently only post attachments are exported. But featured images aren’t always post attachments..
SOLUTION:

function demomentsomtres_add_attachments($post_ids) {
	$attachments = array();
	foreach ($post_ids as $post_id):

+		//****************************
+		//post isnt always parent for a featured image
+		$value = get_post_meta($post_id, '_thumbnail_id', true);
+		if ($value) {
+			$attachments = array_merge($attachments, array($value));
+		}
+		//****************************

		$attachArgs = array(

https://wordpress.org/plugins/demomentsomtres-wp-export/