The problem is alternative routes. If Waze notices a traffic jam on the route, it tries to find alternatives and crashes. You can check for yourself by doing any route and than press the bottom-bar and select alternative routes on the menu that pops up. It immediately crashes.
One thing I haven't figured out is, that it seems to work without gps signal or something. On the road I can never get Waze working. It keeps crashing and crashing. But from inside my house it seems to work from time to time. Maybe it's lack of GPS signal. Maybe it's wifi connection. No idea. But once it's working and I get on the road, it'll look for alternatives again by itself, but doesn't crash anymore.
I just Google would give up their fear for Microsoft and fix Waze for Windows Phone.
Because fear leads to anger.
Anger leads to hate.
Hate leads to ... suffering!