Lightmaps giving opposite to expected results

I am having troubles with lightmaps, i’ve tried quite a few different ways of fixing it. Like starting a new map, checking UVs are on right channel, other settings.
A not ideal fix i have found is putting two different meshes together in a blueprint then the shadows work properly -

In the first image the dark roof models are single meshes with the working objects to the side inside blueprints. It seems the lightmaps are like the inverse to what i’d expect. (dark facing the light and light at the other side)

Any suggestions? Thanks for looking

right click, view image for bigger image.