What is your form action set to?
Try adding this code right after the recordset code:
<?php
if (isset($_POST["Update"])) {
die("Prod URL:" . str_replace("https://yourdomain.com","../..",$WADAcac_prod_subcategory_NEW_update->getColumnVal("prod_url")) ."images/");
}
?>
That will let you see the value that is being set so you can adjust and correct it more easily.