
Apparently steel gets brittle from cold at much higher temperatures than I previously thought. It was maybe -12°C when I broke several bits (from different sets/makes) in a row before giving up. Some of these had driven hundreds of screws before, so they weren't made of cheese.
Ants Pants mentioned this in a video and I didn't believe it because I thought cold embrittlement wasn't a thing until -70°C or thereabouts.