# Frequent Crash: Assertion failed: CellIndex \< CellIndexMax

**URL:** <https://forums.unrealengine.com/t/frequent-crash-assertion-failed-cellindex-cellindexmax/1937603>\
**Category:** Feedback & Requests\
**Tags:** unreal-engine, question\
**Created:** [July 15, 2024, 1:29am UTC](https://forums.unrealengine.com/t/frequent-crash-assertion-failed-cellindex-cellindexmax/1937603 "2024-07-15T01:29:30Z")\
**Posts on this page:** 10\
**Page:** 1

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**Author:** ![Sharkster-NXR](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/sharkster-nxr/32/1194654_2.png) [@Sharkster-NXR](https://forums.unrealengine.com/u/Sharkster-NXR)\
**Post date:** [July 15, 2024, 1:29am UTC](https://forums.unrealengine.com/t/frequent-crash-assertion-failed-cellindex-cellindexmax/1937603/1 "2024-07-15T01:29:30Z")

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The current build (5.4.2, EDIT: And also 5.4.3) has a bug that causes the editor to crash, when very large, partitioned environments with many actors are loaded.

There are some threads on this forum that discuss the issue, like:

> [@Crash UE 5.4 project migration from 5.1](https://forums.unrealengine.com/t/crash-ue-5-4-project-migration-from-5-1/1892286):
>
> Hello everyone, I have a strange crash in 5.4. I have created in 5.1 a big map with world partition (around 1000km2) and when I try to convert my project into a 5.4 project, I have this crash message when it try to open the map, can you help me? Message: “Assertion failed: CellIndex \< CellIndexMax [File:D:\build++UE5\Sync\Engine\Source\Runtime\Renderer\Private\SceneCulling\SceneCulling.h] [Line: 172]”

> [@UE 5.4.2: Landscape Grass Crash](https://forums.unrealengine.com/t/ue-5-4-2-landscape-grass-crash/1899331):
>
> I was trying to migrate a map created in UE 5.1.1 to UE 5.4.2. I migrated it successfully, but when I open it and move around in it, the editor closes with the error: Assertion failed: CellIndex \< CellIndexMax [File:D:\build++UE5\Sync\Engine\Source\Runtime\Renderer\Private\SceneCulling\SceneCulling.h] [Line: 172] I managed to isolate the problem to the LandscapeGrassOutput. To check if it was a migration issue, I created a new project and followed this steps: 1- Create a new UE 5.4.2 project …

> [@Crash with migrated UE5.1 worldpartition project to UE5.4 at the openning](https://forums.unrealengine.com/t/crash-with-migrated-ue5-1-worldpartition-project-to-ue5-4-at-the-openning/1918310):
>
> Hello, after migrating my UE5.1 big worldpartition project to UE5.4, when I try to oppen the new map in UE5.4 I have a crash : “Assertion failed: CellIndex \< CellIndexMax [File:D:\build++UE5\Sync\Engine\Source\Runtime\Renderer\Private\SceneCulling\SceneCulling.h] [Line: 172]” I need Help!!!

The bug is easily reproducible. Make a large, partitioned world and load plenty of stuff into the editor. After it surpasses an unknown limit, it crashes. Some devs assume that it’s foliage related, but I can’t necessarily confirm that.

As we’re affected by this bug and pretty much cannot go on working on our project for as long as this sticks, I reported a bug more than two weeks ago, following these instructions:  
[https://www.unrealengine.com/en-US/support/report-a-bug](https://www.unrealengine.com/en-US/support/report-a-bug)

I instantly received an automatically generated mail with a case number, but that was it. The bug isn’t listed in the bug tracker and I haven’t heard anything back.

What am I (or people affected by this bug) supposed to do now? Does it make sense, to report it again? How long does it usually take until a bug is added to the bug tracker?

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**Author:** ![AXL3D2021](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@AXL3D2021](https://forums.unrealengine.com/u/AXL3D2021)\
**Post date:** [July 16, 2024, 1:58pm UTC](https://forums.unrealengine.com/t/frequent-crash-assertion-failed-cellindex-cellindexmax/1937603/2 "2024-07-16T13:58:23Z")

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Hello, thanks for your post, maybe the bug is corrected in the new 5.4.3, I’m now migrating my project to test

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**Author:** ![AXL3D2021](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@AXL3D2021](https://forums.unrealengine.com/u/AXL3D2021)\
**Post date:** [July 16, 2024, 3:55pm UTC](https://forums.unrealengine.com/t/frequent-crash-assertion-failed-cellindex-cellindexmax/1937603/3 "2024-07-16T15:55:35Z")

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For me it’s still crashing…

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**Author:** ![AXL3D2021](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@AXL3D2021](https://forums.unrealengine.com/u/AXL3D2021)\
**Post date:** [July 16, 2024, 4:03pm UTC](https://forums.unrealengine.com/t/frequent-crash-assertion-failed-cellindex-cellindexmax/1937603/4 "2024-07-16T16:03:47Z")

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It’s charging more than before but nearly at the end it crash

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**Author:** ![Naitguolf](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Naitguolf](https://forums.unrealengine.com/u/Naitguolf)\
**Post date:** [July 16, 2024, 6:43pm UTC](https://forums.unrealengine.com/t/frequent-crash-assertion-failed-cellindex-cellindexmax/1937603/5 "2024-07-16T18:43:23Z")

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yep, crash all the way… before 5.4.2 it did´t!

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**Author:** ![Sharkster-NXR](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/sharkster-nxr/32/1194654_2.png) [@Sharkster-NXR](https://forums.unrealengine.com/u/Sharkster-NXR)\
**Post date:** [July 17, 2024, 12:37am UTC](https://forums.unrealengine.com/t/frequent-crash-assertion-failed-cellindex-cellindexmax/1937603/6 "2024-07-17T00:37:51Z")

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Yup. Good ol’ “Assertion failed: CellIndex \< CellIndexMax” crash still there. Editor crashes when I try to load our world map.

Most worrying thing is the fact that it’s not even on their bug tracker yet. So this game breaking bug may stick around for a looooong time. 💩

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**Author:** ![Quaggles](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Quaggles](https://forums.unrealengine.com/u/Quaggles)\
**Post date:** [July 22, 2024, 1:10pm UTC](https://forums.unrealengine.com/t/frequent-crash-assertion-failed-cellindex-cellindexmax/1937603/7 "2024-07-22T13:10:59Z")

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I think I’ve found a workaround that may be useful until it’s officially fixed.

From my understanding the crash occurs due to a limit being hit in the Nanite Scene Culling code, instead of each instance being culled individually the scene is parsed and grouped into cells so that less bounds checks need to be made. If more than 1048576 cells are created you get the crash.

Two ways you can avoid the crash are:

1. Disable Nanite scene culling by setting `r.SceneCulling 0` this will likely reduce performance so profile this yourself but it let me open my level without crashing to work on it. You can set this in DefaultEngine.ini with:

```auto
[ConsoleVariables]
r.SceneCulling=0

```

1. Reduce the number of cells so they don’t hit the limit, I did this in my project by increasing the minimum cell size from the default of 4096cm to 16384cm with `r.SceneCulling.MinCellSize`, the command is read only so can’t be changed once the editor has launched. You can set this in DefaultEngine.ini with:

```auto
[ConsoleVariables]
r.SceneCulling.MinCellSize=16384

```

My level is large and mostly flying around at high altitudes so having less granular culling was pretty inconsequential for me.

You can use the command `r.SceneCulling.DebugRenderMode 1` to view the cells and see how your meshes are being grouped and then increase or decrease `r.SceneCulling.MinCellSize` in the config restarting the editor each time until you find the best value that doesn’t crash and gives you enough culling granularity.

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<div class="post-metadata">

**Author:** ![Sharkster-NXR](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/sharkster-nxr/32/1194654_2.png) [@Sharkster-NXR](https://forums.unrealengine.com/u/Sharkster-NXR)\
**Post date:** [July 22, 2024, 7:18pm UTC](https://forums.unrealengine.com/t/frequent-crash-assertion-failed-cellindex-cellindexmax/1937603/8 "2024-07-22T19:18:00Z")

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> [@Quaggles](#):
>
> r.SceneCulling 0

I can’t say “Thank you!!!” enough. This work-around finally allowed me to open our world map again. I wonder how anyone could hard-code a limit to the cells being used in an **open** world engine.

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**Author:** ![OldSalty](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@OldSalty](https://forums.unrealengine.com/u/OldSalty)\
**Post date:** [July 23, 2024, 2:48am UTC](https://forums.unrealengine.com/t/frequent-crash-assertion-failed-cellindex-cellindexmax/1937603/9 "2024-07-23T02:48:17Z")

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Yeah this also helped me out! You should mark as answered by The Quaggles!

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**Author:** ![system](https://d3kjluh73b9h9o.cloudfront.net/original/4X/7/1/3/713c9d3f58553f0de89543d76a8a3a2779dc9fa4.png) [@system](https://forums.unrealengine.com/u/system)\
**Post date:** [August 22, 2024, 2:48am UTC](https://forums.unrealengine.com/t/frequent-crash-assertion-failed-cellindex-cellindexmax/1937603/10 "2024-08-22T02:48:35Z")

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