Symptoms
Cancellation order/corresponding invoice does not have SKU attached to refund details even though SKU are configured correctly.
Cause
SKU is added to DeliverLine table at the moment of resource/subscription purchase. The refund is calculated based on deliver lines. So, if SKU was not properly configured at the moment of purchase, then later, on cancelation, SKU will not be added to the refund even though SKU are already properly configured.