Z-fighting on mesh despite no overlapping UVs

I’m currently working on a cardboard box mesh for my map, but it has really harsh z-fighting despite there being a proper(?) UV and lightmap channel.

Here is the mesh inside my map. The z-fighting happens all over the model.

However, it looks just fine inside the mesh viewer.

Also, here is the UV layout in case I’m missing something. Everything seems to be on the grid with enough padding.

Any help would be appreciated. I can’t seem to find anything else about this problem.

Did you set the lightmap coordinate index to 1?

Yep, but that didn’t seem to change anything.

The mesh looked fine when I textured it in Substance Painter. I’m guessing it’s a UE4 issue.

maybe the same bug as this → https://answers.unrealengine.com/questions/574013/what-are-these-black-glitches-in-my-scene.html

Yes, that seems to be the same problem. What’s interesting is that I think he’s using the stock assets from the Realistic Rendering template, but the meshes are still artifacting. I wonder if it has something to do with the editor itself and not the mesh.

Changing my box to movable also removes the artifacts. I wonder what is going on.