[UE 5.8.3][macOS ARM64][MetaHuman] Body DNA export crashes — Pair != nullptr assertion in Map.h.inl:638; Head DNA succeeds

General Issues and Bug Reporting (Unreal Engine)
1

Summary

MetaHuman body DNA export consistently crashes Unreal Engine 5.8.3 on Apple Silicon macOS, while head DNA export from the same MetaHuman succeeds.
The body failure occurs both when exporting externally and when attempting a project-only DNA asset export with no external path, suggesting the failure is not confined to external .dna serialization.
Environment

  • Unreal Engine 5.8.3
  • macOS 27.0
  • Apple M5 Pro / ARM64
  • MetaHuman Creator enabled
  • MetaHuman Creator Core Data installed
  • Character successfully processed through Create Full Rig
  • Rig state: Joints and Blend Shapes

What Type of Bug are you experiencing?

UI / Tools

Steps to Reproduce

Steps to Reproduce

  1. Open a saved MetaHuman Character in UE 5.8.3.
  2. Ensure the character has completed Create Full Rig and is in the Joints and Blend Shapes state.
  3. Create MetaHuman DNA export parameters.
  4. Set DNABody = true.
  5. Set DNAHead = false.
  6. Set a valid new project path.
  7. Leave ExternalPath empty.
  8. Execute the DNA export.

Expected Result

With DNABody=true and DNAHead=false, Unreal should create/export the MetaHuman body DNA asset.

Observed Result

Unreal asserts:
Pair != nullptr
at:
Map.h.inl:638
and subsequently crashes with:
SIGSEGV 0x3
No body DNA asset is created.

Affects Versions

5.8

Platform(s)

Mac

For crash reports, include your callstack

Script Stack (1 frames) :
/Script/MetaHumanCharacterEditor.MetaHumanCharacterExportBlueprintLibrary.ExportDNA

[2026.09.24-21.28.11:651][ 2]LogMac: Error: appError called: Assertion failed: Pair != nullptr [File:Runtime/Core/Public/Containers/Map.h.inl] [Line: 638]

[2026.09.24-21.28.11:694][ 2]LogMac: === Critical error: ===
SIGSEGV: invalid attempt to access memory at address 0x3

[2026.09.24-21.28.11:694][ 2]LogMac: 0x08bc2274 libUnrealEditor-Core.dylib!FGenericPlatformMisc::RaiseException(unsigned int) [UnknownFile])
0x08d863ec libUnrealEditor-Core.dylib!FMacErrorOutputDevice::Serialize(char16_t const*, ELogVerbosity::Type, FName const&) [UnknownFile])
0x08f00a78 libUnrealEditor-Core.dylib!FOutputDevice::LogfImpl(char16_t const*, …) [UnknownFile])
0x08dfc278 libUnrealEditor-Core.dylib!FDebug::CheckVerifyFailedImpl2V(char const*, char const*, int, char16_t const*, char*) [UnknownFile])
0x08df68e4 libUnrealEditor-Core.dylib!FDebug::CheckVerifyFailedImpl2(char const*, char const*, int, char16_t const*, …) [UnknownFile])
0x0f6d81b4 libUnrealEditor-UMG.dylib!_MergedGlobals() [UnknownFile])
0x0f6b4a44 libUnrealEditor-UMG.dylib!_MergedGlobals() [UnknownFile])
0x0f705c5c libUnrealEditor-UMG.dylib!_MergedGlobals() [UnknownFile])
0x0f5f02a4 libUnrealEditor-UMG.dylib!_MergedGlobals() [UnknownFile])
0x072e8d00 libUnrealEditor-CoreUObject.dylib!UFunction::Invoke(UObject*, FFrame&, void*) [UnknownFile])
0x0766cb28 libUnrealEditor-CoreUObject.dylib!UObject::ProcessEvent(UFunction*, void*) [UnknownFile])

0x13291e5c libUnrealEditor-UnrealEd.dylib!UE::Core::Private::Function::TFunctionRefCaller<FTickableEditorObject::TickObjects(float)::‘lambda’(FTickableObjectBase*), void, FTickableObjectBase*>::Call(void*, FTickableObjectBase*&) [UnknownFile])
0x19f25110 libUnrealEditor-Engine.dylib!FTickableObjectBase::SimpleTickObjects(FTickableObjectBase::FTickableStatics&, TFunctionRef<void (FTickableObjectBase*)>) [UnknownFile])
0x1381a908 libUnrealEditor-UnrealEd.dylib!UEditorEngine::Tick(float, bool) [UnknownFile])
0x1437a62c libUnrealEditor-UnrealEd.dylib!UUnrealEdEngine::Tick(float, bool) [UnknownFile])
0x04af91d8 UnrealEditor!FEngineLoop::Tick() [UnknownFile])
0x04afd488 UnrealEditor!GuardedMain(char16_t const*) [UnknownFile])
0x04b14afc UnrealEditor!-[UEAppDelegate runGameThread:] [UnknownFile])
0x08d85ac0 libUnrealEditor-Core.dylib!-[FCocoaGameThread main] [UnknownFile])
0x8cc62ca8 Foundation!NSThread__start() [UnknownFile])
0x8b4a5d00 libsystem_pthread.dylib!_pthread_start() [UnknownFile])
0x8b4a0cec libsystem_pthread.dylib!thread_start() [UnknownFile])

Additional Notes

Head DNA export succeeds from the same saved MetaHuman and has been successfully imported into Blender 5.2.1 ARM64 using Character DNA Free 0.13.8/OpenRigLogic, where facial controls operate correctly.
Body DNA has failed through two materially different configurations with the same Pair != nullptr assertion: direct external export and project-only export with ExternalPath empty.
The project-only attempt was performed once and was not repeatedly retried after the crash. No body DNA asset was created.
A separate complete DCC export is currently blocked by missing texture sources; this appears distinct from the body-DNA assertion.
Full crash log and exact export parameters are available.