UE5 - CPU Lightmass: Assertion failed: BlendMode

Development Rendering
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Hello since UE5 CPU Lightmass often crash with this error:

<None> === Lightmass crashed: ===
Assertion failed: BlendMode != BLEND_Opaque && BlendMode != BLEND_Masked [File:M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\ImportExport\Material.cpp] [Line: 46] 

0x00007ff611c35364 UnrealLightmass.exe!Lightmass::FMaterial::Import() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\ImportExport\Material.cpp:50]
0x00007ff611c0365c UnrealLightmass.exe!Lightmass::FLightmassImporter::ConditionalImportObjectWithKey<Lightmass::FMaterial,TMap<Lightmass::FSHAHash,Lightmass::FMaterial *,FDefaultSetAllocator,TDefaultMapHashableKeyFuncs<Lightmass::FSHAHash,Lightmass::FMaterial *,0> >,Lightmass::FSHAHash>() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\ImportExport\Importer.h:201]
0x00007ff611c382e3 UnrealLightmass.exe!Lightmass::FStaticLightingMesh::Import() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\Lighting\LightingMesh.cpp:145]
0x00007ff611c9a63d UnrealLightmass.exe!Lightmass::FStaticMeshStaticLightingMesh::Import() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\Lighting\StaticMesh.cpp:299]
0x00007ff611c075b4 UnrealLightmass.exe!Lightmass::FLightmassImporter::ImportObjectArray<Lightmass::FStaticMeshStaticLightingMesh,TMap<FGuid,Lightmass::FStaticMeshStaticLightingMesh *,FDefaultSetAllocator,TDefaultMapHashableKeyFuncs<FGuid,Lightmass::FStaticMeshStaticLightingMesh *,0> > >() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\ImportExport\Importer.h:155]
0x00007ff611c368d3 UnrealLightmass.exe!Lightmass::FScene::Import() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\ImportExport\LightmassScene.cpp:207]
0x00007ff611c1b34f UnrealLightmass.exe!Lightmass::BuildStaticLighting() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\CPUSolver\CPUSolver.cpp:179]
0x00007ff611c409d5 UnrealLightmass.exe!Lightmass::LightmassMain() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\Launch\UnrealLightmass.cpp:269]
0x00007ff611c61507 UnrealLightmass.exe!main() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\Launch\UnrealLightmass.cpp:551]
0x00007ff611cd046c UnrealLightmass.exe!__scrt_common_main_seh() [D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
0x00007ffe878374b4 KERNEL32.DLL!UnknownFunction []
0x00007ffe879e26a1 ntdll.dll!UnknownFunction []



0x00007ff611c35364 UnrealLightmass.exe!Lightmass::FMaterial::Import() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\ImportExport\Material.cpp:50]
0x00007ff611c0365c UnrealLightmass.exe!Lightmass::FLightmassImporter::ConditionalImportObjectWithKey<Lightmass::FMaterial,TMap<Lightmass::FSHAHash,Lightmass::FMaterial *,FDefaultSetAllocator,TDefaultMapHashableKeyFuncs<Lightmass::FSHAHash,Lightmass::FMaterial *,0> >,Lightmass::FSHAHash>() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\ImportExport\Importer.h:201]
0x00007ff611c382e3 UnrealLightmass.exe!Lightmass::FStaticLightingMesh::Import() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\Lighting\LightingMesh.cpp:145]
0x00007ff611c9a63d UnrealLightmass.exe!Lightmass::FStaticMeshStaticLightingMesh::Import() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\Lighting\StaticMesh.cpp:299]
0x00007ff611c075b4 UnrealLightmass.exe!Lightmass::FLightmassImporter::ImportObjectArray<Lightmass::FStaticMeshStaticLightingMesh,TMap<FGuid,Lightmass::FStaticMeshStaticLightingMesh *,FDefaultSetAllocator,TDefaultMapHashableKeyFuncs<FGuid,Lightmass::FStaticMeshStaticLightingMesh *,0> > >() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\ImportExport\Importer.h:155]
0x00007ff611c368d3 UnrealLightmass.exe!Lightmass::FScene::Import() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\ImportExport\LightmassScene.cpp:207]
0x00007ff611c1b34f UnrealLightmass.exe!Lightmass::BuildStaticLighting() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\CPUSolver\CPUSolver.cpp:179]
0x00007ff611c409d5 UnrealLightmass.exe!Lightmass::LightmassMain() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\Launch\UnrealLightmass.cpp:269]
0x00007ff611c61507 UnrealLightmass.exe!main() [M:\MMVS_EngineFiles\UnrealEngine\Engine\Source\Programs\UnrealLightmass\Private\Launch\UnrealLightmass.cpp:551]
0x00007ff611cd046c UnrealLightmass.exe!__scrt_common_main_seh() [D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
0x00007ffe878374b4 KERNEL32.DLL!UnknownFunction []
0x00007ffe879e26a1 ntdll.dll!UnknownFunction []

That not the first time I get this issue and the only way I found for fix this to select all materials of my game in Content Drawer → Right click Reload → Right click Save.

Doing this is a huge waste of time. Please do you have any idea why I am getting this issue?

Thank you.

2 Likes
2

Same issue here… Clicking Reload on all assets didn’t solve it. Have you found a solution?

3

This is still the case on UE5.1

4

Also happened to me on 5.1.1

1 Like
5

Same issue on 5.1.1 but I’ve noticed that happens when using assets imported with Datasmith. Anyone using Datasmith and having this blocking problem?
In the same level, removing the Datasmith assets and importing the same geometry using standard fbx format, lightmass works fine