I've had a similar problem before, door wouldn't open randomly from the outside or inside. From what I recall the plastic coating on the door latch had come loose and somehow managed to stop it all from working properly. After getting in the passenger side and driving home it still was doing it. The next morning when I went out to fix it I just pushed the door in as I pulled the handle and it opened right up as normal. Replaced the striker with a new one and it hasn't happened since. Might not be the cause of your problem but it's easy enough to try at least.
