Just guessing, but sounds like the thermostat is bad or the sensor inside the smoker is cracked a little and when it gets hot it expands enough to break connection to the control unit.
I would say that just like any other digital display whether it be a clock, radio, thermostat, watch, or whatever, the display is failing. Sometimes it is the heat (too hot where the display is, like in the sun) and sometimes it is too cold (like cooking in the snow).
