Are we the only developers who think that lightmaps are an indomitable beast in Unreal? We have done all the tutorials http://www.worldofleveldesign.com/ and read a lot of stuff in answerhub, but are still facing really sirious problems.
I have opened a question on answerhub to describe the overall situation:
What do you think about that? What are we doing wrong?
I notice strange anomalies with my light-mapping as well. I suspect it might be due to lack of edge padding, as well as clamping the texture’s edges.
I’m not sure how one would solve either of those issues if those are indeed to blame. I know how to do it if I’m baking lighting in 3ds Max w/ Mental Ray using RenderToTexture, but I don’t know how to do it in UE4.
I’ve checked some tutorials about Lightmap from http://www.worldofleveldesign.com/ recently and I definitely see how you’re ignoring rules from them 
Padding is not 2px, it is tied to your Lightmap resolution, so if your res 16 then you need to have 1/16 space from each side of uv shell. With bigger resolution padding size is getting lower and lower.
Also your uv shells are colliding with borders which is prohibited as well. Add padding to this areas.
Open StaticMesh and in LOD0->Build Settings and play with Lightmap resolution-Apply changes to see how uv shells should be placed
Also, your UV mapping could be better, you have some surfaces that are separated that don’t need to be, plus a lot of things that are distorted so that they end up as rectangle shapes which is not good either. You’ll probably also have to use a higher resolution than 64 for that mesh.
Ok, we will try to follow your advises! Thank You very much! You’re a great help for us!