Directional Light not lighting an object fully after lightmass?

I’m working on a stairwell and everything is going peachy with lightmass minus this one particular bit.
I’ve followed the UE4arch lighting workflow here: https://ue4arch.com/ue4archs-unreal-engine-4-lighting-workflow-part-1/
for lighting my scene.

However one of the corners of my mesh that is directly being hit isn’t getting the light hit baked into it, even though GI is calculated for the supposed hit area on the other meshes.

In the image below, the red scribbled area should be getting hit directly by the sun light I’ve got aiming straight down. Even the GI bounces on the other objects support that it should be lit, and in dynamic lighting before building lightmass it was lit there as well.

That particular floor element has a lightmap resolution of 1024 and it’s got an alright lightmap UV for that resolution. Also pictured below. I’d like to mention this is the only mesh in the scene that has this problem. Everything else is great. :slight_smile:

Any help in solving the issue would be great. I have a feeling it’s due to the size of the floor and the relatively small region being hit directly, but changing and tweaking lightmass settings doesn’t seem to affect the problem area.

After Lightmass

Before Lightmass

UVs