First published by Money Metals here: https://www.moneymetals.com/news/2020/01/27/why-is-the-price-of-palladium-rising-001955

Physical palladium and rhodium markets are buzzing. Reported prices for both metals leapt higher in recent days. The story behind palladium’s move is that a physical shortage has developed in London. Traders sold metal they didn’t physically possess. Now they are being asked to deliver the bars and they are scrambling to secure the metal needed, bidding prices higher.