In the OP, Walls stated that they picked up the Bounty Cache, opened it and got everything they expected… except the Bounty Mats.
If they had left the items on the ground too long, the entire Large Horadric Chest (Bounty Cache) would have disappeared. Not just one item from the Chest.
Another player reported a similar issue. I believe they weren’t receiving the Bounty Mats from Act IV Bounties.