I would agree with Brian. I have had issues where alignment was an issue. It was a little frustrating. A simple test I would try is take the sensor and place the magnet and sensor by the system and see if you are still having the problem. I would wonder if it could have anything to do with the antenna in the unit. Just worth a try. My thought would be if it is working OK as it is closer to the unit, I would then start focusing on the unit being faulty. I would think that, it may be a stretch. But worth looking at.
Let me know if you need anything else.
Mike