My client used TCP to sell items over wordpress website. Shipping method has been setup correctly, and there's no problem with purchase and payment until today. One of order made by a customer doesn't include the shipping cost, and as result the total number only include the cost of the purchased item.
When I checked into administration, in the Orders section, I click the order with wrong shipping method and saw that the Shipping method of that order is empty (blank), and there's no line of shipping cost at all in the total calculation. And also the internal comment contains these lines:
I have checked the shipping method and it's all fine. This issue is the first time, previous orders have their shipping cost included correctly.
Any idea what's going on?