Over the past two months, the success rate of the TouchID key on my Magic Keyboard has been atrocious. I was seriously considering replacing it when, today, I possibly stumbled upon the real cause. My hands may just have been too cold. After it failed on me this afternoon, I rubbed my hands together to warm them up and when I pressed the key again it worked. I repeated it a few times later in the day and, without fail, it would unlock once I’d warmed my hands. I’m gobsmacked, to be honest.