UE5.4 SkeletalMesh error in PopulateMorphTargetVerticesData() due to mismatch between RenderData and ImportedModel

[ninja152play]

When opening UE5.4 IoStore assets in FModel using the latest version of CUE4Parse, all SkeletalMesh assets fail to load. StaticMesh, textures, materials, and animations work normally, but SkeletalMesh consistently produces an error.

Exception occurs in:

System.IndexOutOfRangeException
at USkeletalMesh.PopulateMorphTargetVerticesData()

Environment:
UE version: 5.4
Format: IoStore (.ucas / .utoc)
Tool: FModel (latest version)
CUE4Parse: latest version bundled with FModel
Issue: only SkeletalMesh assets are affected

Working asset types:

StaticMesh
Texture
Material
Animation

Non-working asset types:

All SkeletalMesh assets (with MorphTargets)

Observed MorphTarget data appears valid:
NumBaseMeshVerts differs per LOD (e.g. 1073 / 2080 and 9905 / 15127)
bGeneratedByEngine = true

Root cause analysis:
UE5.4 uses multiple vertex sources for SkeletalMesh:

ImportedModel (raw LOD0 vertices)
RenderData (optimized/cooked vertex buffers)
SkinCache / deformation pipeline

CUE4Parse appears to use RenderData vertex buffers for SkeletalMesh, while MorphTargets are indexed relative to ImportedModel (LOD0). This leads to index mismatch and out-of-bounds access in PopulateMorphTargetVerticesData().

The error occurs when:
morphIndex >= RenderData.VertexCount

Conclusion:
UE5.4 MorphTarget pipeline is incompatible with the current CUE4Parse logic based on RenderData vertex buffers.

[LongerWarrior]

what game?

[ninja152play]

DamselRace

[LongerWarrior]

please also provide mappings file

[ninja152play]

https://drive.google.com/file/d/1G1UzioPoi6MdDu_i5l2PrM_QWzDplG1j/view?usp=sharing