TouchID requires your Password after 48 hours "TouchID requires your Password after 48 hours"


  Update July 2016
  Since posting this question, the message has changed to
  Your passcode is required to enable Touch ID
  &amp; now
  has a documented answer at 
  https://apple.stackexchange.com/a/245796/85275


I just spotted the above message for the first time today. I've had the phone 3 weeks [new 6s] &amp; never spotted it before.

It's not something I need to 'fix' but I wonder if anyone knows what may trigger it; &amp; why it took 3 weeks to ask me for the first time.

.. or, incidentally &amp; totally opinion-based - why it thinks a 6-digit code is more secure than my fingerprint.

Late thought:
Does it do it 2 days after a reboot or OS update?
It's done it just one more time, which was perhaps 48h+ after the 9.1 update.

Current guess is it's "new to iOS 9" which is why people have been seeing it on older devices too.
I'm still convinced I get it once after every update - but it's something I just dismiss without thinking until later, when I've lost the train of thought that would allow me to 'accurately guesstimate' when it was last rebooted.
The first part of your question has to be a glitch. The iPhone 6S is still a little buggy; mine doesn't always play system sounds, like the Siri chime and the lock "click" sound. But I can explain the second part of your questing:

Apple thinks that a passcode is more secure than TouchID is due to the fact that the odds of TouchID giving a false-positive are 1 in 50,000 (stated by Apple). However, the article hasn't been updated after the 2nd-Generation TouchID in the iPhone 6S came out, and given its great speed improvements, I would assume that the 2nd-Gen has a lower chance of giving a false-positive than the 1st-Gen. The odds of guessing a 6-digit passcode, would be literally 1 in 1,000,000. Even the odds of guessing right with 5 guesses, 1 in approximately 200,000 is still higher than TouchID. I like the convenience of TouchID and will still use it everyday, but from a purely statistical standpoint, a passcode is much more secure.