Solved! Go to Solution.
I'm getting the identical message "Add Results Do Not Match" but it is happening when I save to my ArcGISLocalFeatureLayer (via the SaveEditsFailed() call back). I believe the problem is that the backing FeatureClass starts has an extent which is too small to accomodate the incoming Geometry. If I force the first Graphic I add to have the maximum required extent then my subsequent Saves complete successfully.
It would be very helpful if someone on the ArcGISRuntime/WPF could comment on this.