I have experienced this several times over the past 6 months or so, it only seems to occur when connected to the Skyradar, and when switching back and forth between weather, sectionals, and IFR low. It seems the more times you switch back and forth, the more likely. In most instances, the location data and course lines still show up and function, but there's no background (Keeps saying "loading data...."). My latest flight I used the ipad to connect with the skyradar, and not the iFly, and had no problems. I'll try the recalibration prior to my next flight.
T. Murphy