Just simply because Op can't wait for the transaction to be confirmed, I'm using Blockchain wallet and swapping my bitcoin to altcoin, it is quite delayed but after a day the transaction was successfully done and I guess we're the same experienced by the OP.

I don't know what happen to this web wallet, it is more likely they are very buggy wallet that most of them facing the same problem. How can they trust people if there are tons of issues like this?

Good to know even though there's no clarification how did you get it.