Weight based shipping rates issue with draft orders orders

Shopify Partner
20 0 0
A merchant that's using our app recently encountered an inconsistent bug that affects weight based shipping rates in generated draft orders. I'm hoping that the Shopify team or someone here is able to shed some light on this topic.
Basically, weight based shipping rules aren't being applied according to the total weight that is specified in the generated order. This happens only in some cases that we can't unfortunately pack into a reproducible scenario.
Here are some details straight from the shop:
Shipping rules are based on weight
Weight based shipping ratesWeight based shipping rates
--> As you can see in the screenshot the shipping rate for 1lb-2lb is $9.95 and for 2lb-4lb is $11.95.
Image A - expected behavior - generated draft order with the same line items, shipping is calculated as expected ($11.95) - Total weight is 36 oz so it fits within the 2lb-4lb rate
WhatsApp Image 2021-02-23 at 16.35.03 (1).jpeg
Image B - buggy behavior  - generated draft order with the same line items, shipping is not calculated as expected ($9.95 instead of $11.95) - Total weight is 48 oz, the 1lb-2lb rate is applied 
WhatsApp Image 2021-02-23 at 16.35.03.jpeg
To Shopify team members:  would love to share the order id so you could debug the order payload on your end.
Much thanks