Bear in mind that market orders are not supposed to get canceled. Only pending orders are modifiable. The reason is that market orders get confirmed and filled at the current price by the trading venues, with the ultimate goal being instant execution.
It is possible to cancel a market order on rare occasions before a trading venue has confirmed it. Nevertheless, since yesterday’s session was a real roller coaster, if you have any market orders that are pending execution since yesterday, please send me a personal message if you wish for them to get canceled. I will see what we can do on the matter.