Hi guys,
I’ve ******* many issues on my UE4 scene.
As you can see, a lot of light leaks, and I don’t know why. I tried to unfold the lightmap channel 50 differents ways, without results.
I tried too change lightmap resolution ( 512 / 1024 / 2048, boost World settings, production mode etc…)
Initially, it’s Vray scene, but I adapted it to Unreal…
I’m out of idea…Do you have it ?
Have you set up a second UV channel for the lightmaps?
It looks more like a problem due to geometry not having any thickness. The light bleeds severly at the edges!
Make sure that meshes don’t extend beyond each other. For example walls and ceiling need to line up. Otherwise the surface outside will receive lighting and bleed onto the inside, same with shadows.
Cover light entry between joints of meshes so that the light does not enter through the joints fix that
It looks like you have single sided geometry, eg paper thin, even if you line up objects precisely you still need to make some sort of shadowing mesh or temporary outer layer (assign small or none lightmap size to it) you use only for baking then delete it or set it to be not visible in game.
Other problem you might have is you aligned your unwrap to pixels. Unreal shift your lightmap unwrap by 1px so you should align to center of pixels when unwrapping. 
That light leak might be caused by Unreal doing that 1 px offset when packing lightmaps and thus shifting your unwrap in between pixels and producing that leak as result.
Other than that your leak is most likely caused by thin geometry. Try to build shadowbox for it.