not sure why the status session is not being created, but we can use the Log session as well:
<?php if(isset($_SESSION["waue_contact_1_Log"]) && substr($_SESSION["waue_contact_1_Log"],-7) == "Success") { ?>
Thank you message
<?php } else { ?>
<form>
<?php } ?>
<?php if(isset($_SESSION['waue_contact_1_Log'])) unset($_SESSION['waue_contact_1_Log']); ?>