How to Fix Garbled Baked Lighting from Missing Lightmap UVs in Unity

Baked light that smears across seams or bleeds onto faces it should not touch usually comes from lightmap UVs. Real-time materials can reuse overlapping UV0, but the lightmapper needs a second, non-overlapping UV set or it packs neighbors on top of each other.

How to fix it

1. Generate lightmap UVs on import

In the model's Import Settings, enable Generate Lightmap UVs. Unity creates a non-overlapping UV2 by unwrapping the mesh, which fixes most overlap and seam artifacts after a rebake.

2. Tune the unwrap parameters

If seams still leak, open the advanced Generate Lightmap UVs settings and lower Hard Angle or raise Pack Margin so islands have more padding between them.

3. Author UV2 manually for control

For hero meshes, build a clean non-overlapping UV2 in your DCC tool and export it. You get tighter packing and predictable results that an auto-unwrap cannot match.

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 Unity 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.