What causes the Progressive GPU Lightmapper running out of memory?

The GPU lightmapper must fit all lightmaps, the scene's geometry, and atlases in VRAM at once, and a large scene or huge atlas size exceeds the card's memory budget.

How do I catch this when it only happens for some players?

Capture it automatically from the player's device with the full stack trace, the device and OS, the build, and a breadcrumb trail of what they did. That turns a vague complaint into a specific, reproducible issue you can fix without owning the hardware it happens on.

How to Fix the Progressive GPU Lightmapper Running Out of Memory in Unity

Quick answer: Lower the Max Lightmap Size, reduce lightmap resolution, split the bake into smaller scenes, and close other GPU apps. Update the GPU driver if it falls back to CPU.

The GPU lightmapper keeps the whole working set in VRAM, so a scene with many high-resolution atlases overflows the card and Unity either errors or silently reverts to the slow CPU path. Shrinking the working set keeps it on the GPU.

How to fix it

1. Cap the atlas size

In Lighting Settings lower Max Lightmap Size from 1024 to 512 and reduce overall Lightmap Resolution. Smaller atlases dramatically cut peak VRAM during the bake.

2. Bake in smaller chunks

Split a large level into additive scenes and bake them separately, or disable Contribute GI on distant geometry for the pass you are working on, so fewer texels are resident at once.

3. Free up GPU memory

Close browsers and other GPU-heavy apps, and avoid running the editor's high-res game view during a bake. The lightmapper competes with everything else for VRAM.

4. Check the fallback message

Watch the console for the GPU-to-CPU fallback warning. Updating the graphics driver or switching to the CPU lightmapper for one giant scene is a valid last resort.

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.

The errors you never hear about are the ones quietly costing you players. Visibility turns them into a worklist.