Thanks, rinigus. I will try gdb but I have limited experience in that area so there may be a bit of a delay.

Re voice instructions. I may have been a bit unfair. The screen always showed the right way but the voice instructions did not always match. Like when the road was forking, with one fork going straight and one turning right, and I was continuing on the straight line, the voice said turn left. The same on a roundabout with multiple exits. I guess it makes sense from the algorithm point of view but is confusing when you only follow instructions without checking the screen.