How to Fix Lightmap Splotches from Overlapping UV2 on an Imported Mesh in Unity

Blotchy patches on a baked mesh almost always mean its UV2 charts overlap, so two faces share lightmap pixels. Giving the mesh clean, non-overlapping lightmap UVs removes the splotches.

How to fix it

1. Generate lightmap UVs on import

Select the model, open the importer's Model tab, tick Generate Lightmap UVs, and apply. Unity unwraps a non-overlapping UV2 automatically, which is enough for most props.

2. Tune the unwrap parameters

If charts still bleed, expand Advanced under Generate Lightmap UVs and raise Pack Margin and Hard Angle so islands get more padding and split on real seams instead of merging.

3. Author UV2 in your DCC tool

For hero meshes, unwrap the lightmap UV manually in Blender or Maya keeping every island inside 0-1 with no overlap, then disable Generate Lightmap UVs so Unity keeps your channel.

4. Rebake and verify in the UV preview

Open Window > Rendering > Lighting, clear baked data, and rebake. Use the Lightmap UV preview overlay on the mesh to confirm charts no longer overlap.

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.