Screen becomes unresponsive, journal shows timetravel to the future
Without user interaction screen becomes unresponsive to power button, touch, volume keys, bluetooth keyboard. The illumination of the screen has been switched on. The journal (via serial console) shows some errors and a change of date and time.
'systemctl restart phosh.service' re-enables the UI, but the time is still wrong.
After 'reboot' the clock is set right and UI starts as expected.