One incident that really stands out for me was BitMEX conveniently having "server issues" at one point during the March 2020 crash. Their liquidation engine was

One incident that really stands out for me was BitMEX conveniently having "server issues" at one point during the March 2020 crash. Their liquidation engine was hammering the price down - then they took an outage - when they were back up BTC recovered.