Unable to log in after changing local Password

Hello all

I went to to store and bought a YubiKey to us for authentication and to use with my laptops.

Macbook Pro Retina 2012(Yosemite), MBP Retina 15" 2015(ElCapitan)..

It is configured with a static Key, 26 chars.

My Macbook is running Yosemite, signed in to appstore, Icloud and so forth.

When i change to use the 26 char password on my local computer, not use with icloud, it works perfekt for a couple of hours.

But then the next day i'm suddently unable to sign in?!

I'm am 100% sure the password is correct, this same thing happend on two computers.

Why does it work in the beginning but then fails after a couple of hours!??!

Thank in advance