I think this happened to me last night. I had multiple power interruptions that were no fault of the iFly (other than it doesn't have the internal battery :)) and one of the resultant restarts showed no map. I'm pretty sure I tried to select other maps, TAC, Vector, WAC, all to no avail. It seemed to be tracking fine, giving me the distance and direction to my waypoint/destination. I don't recall it happening before, and it cleared up with a reboot.
If it matters, I did the automatic update by putting the SD Card in the computer and updated everything other than the weather and TFR.