I agree it depends on the cuts in the call, but turkeykiller hit it on the head in suggesting that it could be because one of the "flaps" in the cut reed is folding over and sticking. Another possible cause is blowing too hard, or forcing too much air over the reed, causing it to fold and stick at times.
As the reed latex becomes fatigued over time, this problem can get worse and finally make the call unreliable. Sometimes you can cut the leading edge off of the flap to shorten it slightly and this will alleviate the problem. Doing that may also change the sound of the call, though. However, sometimes it changes the sound for the better.
As I have said before, never toss a call that does not suit you without trying to make it sound better by modifying the reed cuts first.
