So on first Build I get an error saying my Lightmaps are overlapping 73%!!
Some googling watched this for a solution UV Lightmap are Overlapping - Resolve issue - UE4 Blueprints - YouTube
Checking the UV in the Mesh Editor I see that the UV index is correctly defined as 1 but my Lightmap index is only 64. Also a visual inspection of the UV shows nothing overlapping.
So I increase the LM resolution to 1024, do a 2nd build and now get an error saying my Lightmaps are overlapping 4%.
Repeat a 3rd time with LM resolution to 2048 and get an error saying my Lightmaps are overlapping 2%.
My question is
Is 2% overlap acceptable or must it be 0% overlap?
and
How do you achieve 0% overlap without increasing the resolution to unacceptable values?