Between August 25 and August 31 there were some issues with orders where a customer had ordered several different items within one order from one partner. When a single order was requested via the API, we may not always have returned all orderItems in the response at that specific moment. When a specific orderId would have been retrieved later via the API, all orderItems corresponding to the specific orderId would have been returned.
The problem has been solved since 31-08 14:00. From that moment on, all orderItems that belong to 1 orderID will be returned correctly again. We would like to advise you to double-check in the seller dashboard if there are no more open orders for orderItems that may not have been returned via the API. Our sincere apologies for the inconvenience.