I don't seem to be having any issues with the maps app in windows 10 mobile preview. I was looking for HERE maps in the store but couldn't find it. So last week, I decided to test out the maps app and compare it to HERE Drive+. I had maps on my Lumia 920 and HERE on my 520. Everything was the same, like literally, except for maybe a 0.5 sec difference between the voices telling you what to do next. The UI looks same, the voices were the same, speed limit warnings the same. It all makes sense because Microsoft is licensing HERE maps now and have made it better by integrating HERE maps and drive+ into one app.