Stop losses don't always work. When a million people have the same SL at the same price, who do you think should get the money if there's not enough liquidity?
Make your stop losses loser, or if you can do a market sell stop loss even better. Or use phone alert.
I am not talking about price slippage, the stop market order just didn't trigger at all and need to close it manually using limit order, the server thinks it is a short sell on a SSR(short sale restriction) stock