you might've screwed yourself on this one: what happened is the item server took a moment to grant you the item, if you'd have waited it would've eventually given it to you (albeit with no notification that you got it, this has been happening to me with vault items), and because you rerolled in the time it took the server to exchange the item, the new roll took priority and you got a different drop instead because as far as the item server was concerned, you hadn't opened the crate yet.