Since the Lollipop update, I have, on 4 occasions this week, come across the same problem.
When there is an incoming call, the phone does not ring, I only see the screen and notification light turn on.
Phone volume (using side keys) is set to the maximum level for ringer. I go to Settings->Sounds to select my ringtone, and try calling my phone again but each time it remains silent.
When my calendar has notifications, I hear the notificaiton noise for events.
The only way to remedy this each time was a reboot of the phone - after this the ringer would work again, at least until the next time it goes silent.
Any idea what could be causing my phone to remain silent for incoming calls ?
