Hrm, interesting. Well, my next theory would be a build issue of some sort. Being that the phone lost cellular service and contact with Touch ID, sounds like a driver related issue. Possibly a driver missing, or a bad #ifdef still enabled to cloak the existence of the iPhone 6 during development. Or a separate branch for the iPhone 6 that wasn't integrated back properly.

I like looking into failures like this to learn how to try and prevent such in my own workplaces. I'm thankful the products I've worked on do not have anywhere near the public visibility of Apple though.