The map and routes are subject to editing problems and vandalism. There are few protections against this. We have been lucky so far that there have not been widespread issues. This is surely a negative of using a navigation solution that is based on community map updates.
I suspect that if we start to have more problems Waze will be forced to implement a better system to protect the map. They tend to wait until things become a problem before taking action.
The challenge for Waze is how to protect the map but not to prevent community map editors with good intentions from contributing.
San Diego, California USA and Tijuana, Mexico
iPhone 7 Plus, iOS 10.2, Waze 4.16