I've experienced similar. Every time Waze makes a sound, either talking, or just alert sounds, it cuts out the driver's side or front speakers, in order for you to hear the alerts clearly. When the alert is over, the regular sound returns to the front speakers. One time the sound never returned to the front speakers and I was not able to get the sound back until I turned off the car and restarted it. I did not want that to happen again so I just turned off all sounds in Waze. I know that is a crappy solution but that is my fix until a better solution comes up.