My nav screen, since the day after delivery, is just a grey grid. Other 4G services are working. And if you zoom to JUST the right level on nav, the map comes back in certain neighborhoods. The red arrow (indicating my position) still updates, so the computer is working. Seems like the 4G isn't updating the map somehow. Is this a known issue? I did a search here and found one thread from early 2014 with folks saying, "Call it in."