I was using WAZE (current version) on my Moto X (original) running Lollipop 5.1. 5.1 was updated on my phone on 9/14/2015 and WAZE worked flawlessly for a month with 5.1. I have had no issues with my phone or Waze and have been using it for 18 months. The issue began while I was driving and using Waze. The app stated, "Waze is not responding, do you want to WAIT, Close". I did not touch phone, I was driving. In a few seconds my phone rebooted. When it rebooted the phone took over one hour to boot up- it had on screen: Android is starting Optimizing apps 1 of 112 (and it slowly progressed through all apps). When it finally rebooted, I opned Waze.
I didn't find the right solution from the Internet.