I ran into this a lot coming from blender/not being familiar with lightmaps/ue4.
+Make sure that your UV’s are spaced enough so that they don’t overlap. If they overlap, you’ll get that blackness. UE4 generates a light map, sometimes it overlaps in the UV’s… so as Darthviper said, make sure you’re using the non-overlapping UV – it looks like you could space out yours a bit more just to be safe. Just nudge them a few pixels away from eachother… might also help. in ue4 – Double click on the object, and you’ll see options to view UV channels in that viewer window that pops up. It will say 1 or 0. Then you can select which channel you want in the properties.
It may have thrown an error on import, maybe smoothing groups and something like “overlapping UV’s channel 1” Which I thought for the longest was my UV’s made from blender, I kept re-uving… but it turned out that UE4 was defaulting to a channel that had its created lightmap, which had overlapping uvs.
I was trying for hours to “clean” up the model in blender, but it was just the UV’s. UE4 uses UV’s to bake lighting to. So depending on their setup/resolution, that has an effect on your shadows inside of the engine.