Location altitude and latitude 0.0

Hi, 

I recent found the location becomes 0 sometimes, do you have similar issues?

My code is below:

var activityInfo = Activity.getActivityInfo();
var location = null;
if (activityInfo) {
location = activityInfo.currentLocation;
}
if (location) {
location = location.toDegrees();
gLocationLat = location[0].toFloat();
gLocationLon = location[1].toFloat();
if (gLocationLat != 0 && gLocationLon != 0) {
Storage.setValue("_gLocationLat", gLocationLat);
Storage.setValue("_gLocationLon", gLocationLon);
}
}
The result in invocation link &lat=-0.00&lon=0.00. So weird?