Two sided magazine lighting artefacts.

I’ve made this opened magazine mesh:

I’ve imported it to unreal, set up a subsurface two-sided material, set up lightmaps, tried to bake the light to see if everything is alright… and it’s not. It’s not alright at all.

For some reason, I get this as baked light:

Lightmap resolution for this mesh is fine:

What could be the issue? I remember making opened notebook similar to this in the past, and it worked fine.
I even went back and opened an old project of mine to see how I set it up there. Everything seems to be exactly the same as I did now, but there it works fine.:

Lightmass settings I’m using:
image

I can’t figure out what went wrong… Any suggestions? Thanks in advance.

Is it GPU lightmass and one sided geometry?

Default ue4 lightmass.

I tried both one-sided geometry with two-sided subsurface material, and adding thickness with standard material.
The problem with thickness is that those are paper pages… so I can’t really make them thick enough to make the difference.

I guess I’ll just have to compromise, get rid off separate pages altogether and make the whole thing one monolithic “brick” instead >_>

After some extensive testing, tweaking geometry, lightmaps, and just experimenting with stuff to figure out how to correct this issue, here’s what I discovered.

I have this mesh of a magazine with curled cover:

Unreal doesn’t like it at all. Baked light for it gets all sorts of screwed.

However, if I split it into two pieces - the cover, and the block of pages, it fixes the lighting issue.
The problem is - now I have one more draw call for a small prop. Which is not ideal.

I tried to combine two pieces in maya, without merging vertices, but that only led to the same result as before, with one whole mesh.

I tried to combine two pieces in unreal with Merge Actor Tool, and, weirdly enough, that gives different results. There’s no more shadow bleeding, but there’s no occlusion either.

Here’s what I mean:

As you can see, two separate pieces look as we would expect - with all the shadows and occlusion in the right places.

Merged prop is missing occlusion. And I noticed that at some angles it still gets a bit of shadow bleeding.

And a single mesh, exported to unreal, is just awful.

This behavior is weird to me. I’m don’t have technical knowledge to explain what’s happening.

A bunch of copies of a merged actor to show that at some angles it still bleeds shadow.

Once again, as you can see, only the prop consisting of two separate meshes has correct shadows.