Not as software bug or many more would be complaining about this. But it is impossible to truly troubleshoot without knowing device and OS versions. Different devices even from the same manufacturer have different issues. Kulkatz's advice is the best we can give without knowing OS or device.
There are device models with weak internal GPS receivers and you would be best served getting an external receiver (like the Dual150 GPS), an example of this is a Galaxy S I, and the sister Epic 4G devices. But later Samsung devices fixed this issue. If you are getting the target circle rather than the car icon, Waze is not getting the GPS data, check in other apps, also if using Android, try turning off the "Use wireless networks" setting in locations. It's not common but. Have seen problems during a handoff between cell towers and if you are right at a handoff point, your cell maybe bouncing between towers and that confuses the agps at times. However the last few versions of Waze haven't seemed to have that problem, but it has been an issue.
There may be other external interferance sources near you as well. I know of one location that will throw the no GPS message and then lock my device every time I drive there. It only and always happens in that one location and that tells me something near there is throwing interferance.
But for more specific trouble shooting device make, model and OS and version are needed.
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