UV or not UV unwrap when exporting models from Blender to Unreal: when and why

[cyaoeu]

@csimeon;729759

What version is this?
Did you have the seams already created in Blender? Like darthviper says
In my case it seems Unreal created the channel in addition to the two I had already, from Blender, but that was empty despite the fact that I had the same seams.

Yes, the normal UVs only, I only had one UV map and let UE4 generate the second UE map for the lightmap. You can try removing your lightmap UVs and letting UE4 do the work for you.