LoadVRMFileFromMemory crash in Standalone play

[ZeyrinPixel]

Disclaimer:

I spent a long time working through this issue on many different attempts, so this report is a best attempt at collecting the actual changes that fixed it. Was also working on issue #569 during this so they may be related.

Description

Loading VRM files at runtime using LoadVRMFileFromMemory with SetImportMode(false) crashes in UE 5.7 standalone builds. Works in PIE.
Seems to be a result of some PostLoad changes in UE 5.7?

Environment

• Unreal Engine: 5.7
• VRM4U Version: VRM4U_5_7_20260219
• Platform: Windows

Reproduction

1. Set VRMConverter::SetImportMode(false)
2. Call LoadVRMFileFromMemory() in a standalone build
3. Crash occurs

Crashes

Location	Error	Line
LoaderBPFunctionLibrary.cpp	Assertion failed: Pair != nullptr (PostLoad)	~841
LoaderBPFunctionLibrary.cpp	Assertion failed: Pair != nullptr (VRMSetPhysicsAsset)	~847
VrmConvertMorphTarget.cpp	EXCEPTION_ACCESS_VIOLATION (GetCurveMetaData)	~439

Root Cause

Runtime-created skeletal meshes in UE 5.7 have uninitialized internal state:

• SkeletalMesh->PostLoad() fails - mesh description not created
• USkeleton->GetCurveMetaData() fails - internal TMap not initialized

Suggested Fix

Wrap operations in IsImportMode() checks:

LoaderBPFunctionLibrary.cpp:

if (VRMConverter::IsImportMode()) {
    out->SkeletalMesh->PostLoad();
}
if (VRMConverter::IsImportMode()) {
    VRMSetPhysicsAsset(...);
}

VrmConvertMorphTarget.cpp:

USkeleton* skeleton = VRMGetSkeleton(sk);
if (skeleton != nullptr && VRMConverter::IsImportMode()) {
    // curve metadata code
}

Also need to call PostEditChange() (editor) or InitResources() (runtime) when bSkipMorphTarget=true, since ConvertMorphTarget normally handles mesh finalization.

Workaround

Partial: Set Options.bSkipMorphTarget = true and Options.bSkipRetargeter = true. PostLoad crash still requires plugin modification.

[ZeyrinPixel]

I should specify: This is not a complete fix, it only prevents the crash, but also makes several of the optional assets that I need impossible to generate in runtime so a better solution is needed.