OK, so I sent a small announcement to just five people and they went without issue. However, when I sent to the whole church, a total of thirty, including the previous five, they were all marked as unroutable.
Also get this message:
Warning: in_array() expects parameter 2 to be array, null given in /home/customer/www/praiseway.uk/public_html/wp-content/plugins/church-admin/includes/filter.php on line 650