GTT orders have always failed me!
I have used GTT 2-3 times, and it has never filled my order after triggering, despite having sufficient buffer between trigger and limit prices (which always gets me filled in normal SL orders). I lost a big chunk of profits today due to this. It shows the status as "Filled," but it did not actually fill in reality. In the normal order book, it is showing the limit order as "Rejected" because it treated the Sell order as shorting the Option, and thus expected there to be a large enough margin in the account, rather than recognizing it as an exit of the existing bought position.