According to Coinmetrics, none of the major stablecoins became seriously unpegged during the May 19 crypto flash crash. As prices drop, investors often rush to trade their crypto-assets into stablecoins, while the liquidations can cause stablecoins being used as collateral to be sold. This sudden shift in supply and demand can potentially knock stablecoin prices from their $1 peg, and threaten their stability. Although I and some others observed some USD stablecoins below 90 cents on some trading screens, apparently none actually traded there.