0. Volla phone, latest OTA update, stable branch.
1. Power on the phone, wait until it boots up.
2. Enter SIM pin, unlock the phone with phone pin.
3. Lock the phone with power button.
4. Press the power button to unlock the phone, observe the Unity booting screen, wait for it.
5. Enter the phone pin and unlock successfully.
After that every unlocking starts with reboot (step 4).
Side effect or symptom: fingerprint reader stopped working at all, trying to erase fingerprints crashes Settings program.
Where to look for details?
(syslog is useless, even if you filter out every light sensor message)