About the unlock of Sailfish X by means of fingerprint:

Now I understand the behavior better.

First: to use fingerprint unlock you first have to apply a lock code to protect your phone before you can use the fingerprint feature (so it will always be possible to unlock by entering the code on the touch screen in case finger print sensor doesn't work)

Second, unlocking a locked phone: When presented with the lock code sceen it is possible to unlock the device by fingerpint scanner (double function of the power on / off button)

This seems to work with my device only if I patiently and slowly put my finger on the sensor and if nothing happens the first time (as is mostly the case) lift it and put it down on the sensor again, as widely covering the sensor as possible.

Impossible to use efficiently in stress situations and all weather circumstances I can imagine..

Also the placement of the fingerprint sensor of the Xperia X is not helping efficiency, especially when a case is used to protect the phone as the button is laying even deeper.

EDIT: immediately after practicing with unlocking by finger print, I went on trying to input another 3rd fingerprint. This doesn't work. After trial unlocking the phone by fingerprint doesn't work anymore but after the 10th or so time. A messag pops up above the code input: Locked, adjust your grip. I am holding it wrong