I like to trade during major economic data release. When I place Buy stop or Sell stop, then order did not execute when the price cross the entry price. The order still in the pending order row. But when I try to delete the same order, it never delete. But after some seconds, the same order was executed at the same price. But mostly that order results in loss.

Asper the customer care report, it happened due to slippage. If it is due to slippage means, it would open some pips above or below the entry price. But the order was executed in the same price, only after 15 or 30 seconds.

Can anyone explain why this happens???