I have orders where the total quantity was changed manually after an order is placed. I am trying to get the "fulfillable_quantity" for order items through the python api. It works for all orders except for order that have been archived. I am able to get all other information except for this field.
order.line_items.fulfillable_quantity # returns 0 even though in order on website shows the changed quantity
I just tested using our REST and GraphQL APIs using a simple client and was able to see fulfillable quantity with both regardless of the orders archival status. This makes me think this might be something specific with the Shopify Python API. If you are still having issues with this, I would suggest you open an issue on that repo.