Unset only cart session and not ALL sessions
While previous solution works, it generates an issue with logged users.
When a loggedin user completes an order, by using session_destroy(); we kill the logged in session too so he needs to login again.
What I tried and it works I unset the session being created when we configure the Store Cart Summary in Database.
So in my success page (when order has been complete) I just add unset($_SESSION['latestPlacedOrderSessionName']); and this avoids any orders overwrites, but without killing all sessions