Applying Q2 price changes to BDO-reported Q1 holdings estimates a −$2.805B gold effect ($4,668.06 → $4,008.02/oz) and a −$0.928B bitcoin effect ($68,193.95 → $58,642.15): about −$3.73B combined, leaving roughly −$0.48B of the implied −$4.211B result unexplained.
Reported gold-and-bitcoin value fell only about $1.82B because Tether added roughly 14 tonnes of gold and 1,796 BTC. Those purchases partly offset the price declines; the net holdings change is not the same as the mark-to-market price effect.