No doubt in my mind that heavy frost covering the motion glass could prevent motion detection. I've had the same problem with a heavy morning dew at times. Also, some batterys just do not work well in extreme cold, especially alkalines if they are a littledischarged or old. Might explain why they worked after the warmup. My cams take 2 AA batterys and I'm using Sanyo Eneloop rechargeables and have had no cold weather problems at all.I'm convinced lithium batteries are the best when dealing with low temps.
Just my ideas on what may be the problem. And my ideas are sometimes "suspect"....