Thanks Tim -
I am not really in a position move up to 4.10.
I did however find something related to the problem I think.
This is really strange but has something to do with procedural foliage. When the procedural foliage is pushed beyond a certain point, (not quite sure what that point is 
), is causes the lighting to break. You saw my broken “blank” scene with only two elements in it. Removing all of the procedural foliage elements from the scene will not remove the “infection”. I rebuilt my scene piece by piece and confirmed the procedural foliage was corrupting the lighting. I know this is not much of a solution. However, if anyone else encounters this problem they should roll back to a version of the scene before procedural foliage and proceed with caution.