Can you please clarify are you saying that when you initially get in the vehicle and try and turn the ignition key to key will not work in the lock cylinder? If or When this happens have you tried to move the steering wheel (forcibly as you attempt to turn the ignition key?
Have you tried any other keys do they make any difference if you use them? Does the steering wheel move ever so slightly and you can feel it against the lock in both directions?
At this point it sounds like the ignition lock cylinder is worn out or has gone bad again. There are a couple of options that you can try before you replace the ignition lock cylinder. One is spray WD-40 down into the lock cylinder then use compressed air like you would use to clean your keyboard and blow the lock cylinder out. Do this a couple times with WD-40 and compressed air and see if you can free up the lock cylinder otherwise you will have to replace the lock cylinder again. If the tumblers are sticking or binding it will not allow the steering wheel to unlock or the ignition switch to turn.