How to Fix Lightmap Seams Between Separate Modular Pieces in Unreal

When wall and floor modules meet, each owns a separate lightmap and the baker has no idea they should match, so a seam appears at the seam. Raising resolution and enabling seam healing fixes it.

How to fix it

1. Raise the overridden lightmap resolution

Select the modular static mesh instances, and in the Lighting section set a higher Overridden Light Map Res (for example 128 or 256). Larger texels carry less gradient error across the joint.

2. Enable lightmap seam healing

Open the static mesh asset, and under Build Settings tick Generate Lightmap UVs and enable seam fixing; in newer versions the static mesh has a Lightmap Seam Healing option that smooths adjacent texels.

3. Snap pieces to a consistent grid

Position modular kit pieces on the same world grid so their lightmap texels line up. Misaligned offsets put a half-texel discontinuity right at the edge.

4. Rebuild lighting with the production preset

Run Build > Build Lighting Only at Production quality. Preview quality undersamples and exaggerates seams that disappear at full bake settings.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every Unreal Engine error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.