Why a single SKU of my order is shipped by EMS since I choose airmail as the shipping method for the whole order?
This is because this SKU must be over 2 KG (exceeds airmail’s limitation for weight). For such SKU, Cub will ship it via EMS separately. Normally, EMS fee is covered by the price. But for some countries in South America, East Europe and Africa, additional shipping fee will be charged due to the high EMS fee.