Be more specific! Is it locking to the rear with the chamber open after firing the round. Or is it locking up in battery (Slide Closed).
If it is locking to the rear it may be your grip. You may be contacting the slide lock with your thumb when the recoil occurs. Causing upward preasure on it and locking the slide to the rear on occassion? This is not uncommon if the grip is not correct!