Hi @newbie_01 ,
Thanks for your post. The two listings coming back in the return result are for the different inventory states that were adjusted by the change (‘available’ and ‘on_hand’), there’s a great reference about the inventory state labels here: [Shopify Docs: Inventory State Chart]
About quantityAfterChange returning null, that doesn’t seem like the expected result and we have been able to replicate so a report has been filed for further investigation.
Thanks and hope you have a great day,
Jon551