[mothered]

Whether StockX like it or not, if an item goes missing inbetween their authentication warehouse and your delivery address they are responsible for it

I'm not referring to that (the "In between"), but rather this:

ONCE THE ITEM IS AUTHENTICATED AND DELIVERED

The person taking the hit would be StockX or the courier, so it wouldn't matter in this scenario.

Until StockX reimburses the seller, he/she will Initially take the hit.