Any casino that has instant deposits without zero confirmation experience this inconvenience before. I remember experiencing it myself accidentally way back when Bitcoin network was flooded by transaction.
I already lost my bankroll on the casino while my Bitcoin deposit transaction is still pending that later on canceled the transaction.
I still redeposit the lose amount on the casino since I like playing in there. But casino in early days offer 0 confirmation instant deposit that’s why they frequently being abused but I don’t remember a casino suffer a huge loss from this method.