I've had this happen a few times, at least on my old 2 stroke it had to do with the lube getting thick on that spiral gear that engages the flywheel, it is forced into the flywheel against a thin spring by inertia of the starter spinning. Cold weather the lube gets thick and it just spins without engaging the flywheel, shot of WD 40 will get you going until you can replace the lube with something thinner in cold weather.