Touch ID forgets fingers after 12 hours of not being used

So I got my parents a nice iPad Air 2 with cellular data, a great product. The three of us each added a finger and the Touch ID worked fantastically for several hours. However the next day it wouldn't remember neither my mom or dad. It did remember my thumb, but then that stopped working a couple hours later.

We have each added a finger several times. However the pattern is the same. The Touch ID forgets our fingers after about 12 to 24 hours of not being used.

My brother seems to have no problems with his iPhone 6s. His device is also running iOS 9.1.

I conjectured that maybe the problem was that Touch ID didn't like multiple people using the feature to unlock the same device.

Anyway.. now that I, exclusively, have been using my new iPad Pro (cellular) my theory is different.

The pattern is the same.. Touch ID works great immediately after adding a finger but the next day stops working.

My current theory is that it works better with phone than iPad because iPhone users tend to use their device more continuously than iPad users.

iPad users (at least myself and my parents) often let the iPad sit unused and locked for 12 to 48 hours..

I think Touch ID needs frequent use to continuously retrain itself to the "added fingers".

Perhaps, maybe iOS 9.1 is buggy with regard to Touch ID. Maybe a future update can fix this.

Or perhaps, just the cellular version of iPad exhibits this problem.

All things considered, I'm not discouraged with these products they are worth every penny.

FaceTime using iPad Air and Pro is an incredible experience.

I have submitted feedback to Apple: https://www.apple.com/feedback/ipad.html

I encourage anyone else having problems to kindly direct their concern to the feedback page..

Do any of you iPad users have any great tips?