Two orders were created for what the customer says was one purchase.

This is normally a checkout session issue rather than a duplication in Brink. It has been observed when a shopper begins completing an order, closes the checkout window, returns to the cart, changes a delivery option and completes again. Because the first attempt was never confirmed back, the session could not be locked and a second order was created. Check whether both orders share a session before treating it as a system fault.