Kim is right. Once you click Confirm, the checkout_process code is executed, but it will automatically take you to the checkout_success page if payment authorization is completed properly. If payment fails, it'll take you back to the checkout_payment page to re-enter your details.

So ... checkout_process "runs" ... but you never see it.

If your orders are not completing properly, then you have apparently missed upgrading all your scripts properly.

To assess in more detail, I'd work through things this way:
http://www.zen-cart.com/wiki/index.p...Obscure_Issues