It appears that the widespread issues with the fingerprint scanner are caused by the faulty hardware supplied to Sony by the scanner manufacturer and the only way to fix that is to replace the phone under warranty. Unfortunately there is no way to check if the unit is faulty without booting it up and entering the service menu so prepare for several exchanges until you get a working one.

Please follow this steps to see if you are affected and if yes, log a warranty claim with the seller of your phone:

1. Enter the following code *#*#7378423#*#* into the dialler.

2. Click on "Service Tests"

3. Scroll to bottom and click on "Fingerprint Test"

If the status of your fingerprint sensors shows as "Sensor not OK" like this then you got a faulty unit and you should make a claim under warranty.

It seems that Sony strategy of "cheap components in and expensive packaging" haven't changed since Xperia Z1 and as usual we are the ones paying the price...