Hello Unreal peoples,
I’ don’t know if it’s a normal behavior of the engine, but when I bake my lighting (even in production quality) my lightmaps UVs get messed up !
I did a pixel perfect lightmap in Modo, to reduce bleed as much as I could. In “Lightmap Density” viewmod, everything is as intended, until I press “Build”. When the engine apply the lighting, the lightmap density viewmod show the checker texture moved by 1/4 or 1/2 pixel. And my lighting is kind of messed up ! 
How can I correct that, because even with trying to put that corner on pixel perfect (I even predict the 4 pixel DTX compression and place the seam at the edge of a groups of 4 pixels in my UVs) it still doing this and I can’t get a proper lighting !