[bonestamp2]

Fair enough, and if this has only been happening in the last half year and it doesn't always happen... from my experience, I'd be looking at hardware first. It only happened the past 6 months? You mean the coldest 6 months of the year? Hmmm, is one of the sensors or its mounting hardware susceptible to cold weather? Perhaps a sensor was calibrated properly, but it's just barely within the calibrated range and cold weather is enough to push it out of calibration. Perhaps the sensor is defective and the cold is causing it fail prematurely. I wouldn't rule out software, but this sounds more like a hardware issue to me.