I noticed the time was wrong on the clock screen-saver yesterday. I was able to unlock the phone using the mechanical slider, but couldn’t do anything with it, none of the menu options worked and the touch screen was non-responsive. So I had to press the power button for about 5 seconds until I felt the little vibration and the phone shut down.
After powering back up, exactly the same thing happened. Unlock it and it was completely unresponsive. It took a second power-cycle before the phone would start working again. All of this fiddling wasted about 5 minutes while I was in a service station off the M1 trying to check my emails. Very frustrating.