How to Fix Lightmaps Being Shared Wrongly Across Prefab Instances in Unity

If every copy of a prefab shows the same baked lighting regardless of where it sits, the instances are sharing lightmap data. Marking each as a distinct static contributor and rebaking gives each its own region.

How to fix it

1. Mark each instance Contribute GI

Every prefab instance that should bake must have Contribute GI and Receive Global Illumination > Lightmaps enabled, so the baker assigns it a unique atlas slot.

2. Give a sane scale in lightmap

Set a non-trivial Scale In Lightmap on the mesh renderer; a value of zero collapses the instance into shared texels and copies one instance's lighting onto all.

3. Avoid forcing shared lightmaps

Do not reuse a single baked lightmap index across instances (a manual optimization); let the baker pack each instance separately unless they are truly identical in place.

4. Clear and rebake

Clear baked data and rebake so Unity repacks the atlas and assigns each instance its own lightmap UV offset and index.

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.