Huh. I had the same problem with a Sierra work truck. It seemed to go off pretty randomly. It would say the left-rear would be low, or something. I'd check the tires with a gauge, and they'd be all within spec. I never could figure out why it happened.
Didn't seem to be related to how cold it was out, or anything else, as far as I could tell. Just finnicky, I guess. Maybe it's just to trick us into checking the tires with a proper gauge once in a while?