While using Mutable with MetaHumans in Unreal Engine 5.6, we are encountering an issue after generating the Mutable skeletal meshes.
At runtime, the head skeletal mesh bones appear to collapse or “snap” onto the parent body mesh, losing their expected offset.
Visually, the head bones seem to shrink toward the body origin instead of remaining properly attached via the neck/spine hierarchy.
Both the generated body skeletal mesh and the generated head skeletal mesh appear correct in isolation:
- the skeleton assets are valid,
- the MetaHuman bone hierarchy is preserved,
- reference poses look correct outside of runtime.
However, at runtime, the head bones are repositioned as if:
- all bone poses (including body and deformer bones) were being copied onto the head,
- rather than following the standard MetaHuman setup where the head is attached to the spine/neck chain with preserved local offsets.
As a result, all head bones are dispatched to the same transform space as the body bones, breaking the MetaHuman head/body separation and causing incorrect deformation.
Additionally, in runtime, the Animation Blueprint associated with the generated skeletal mesh does not appear to tick, as no events are recorded in the Rewind Debugger. This suggests that the animation update may not be executed properly on the generated Mutable skeletal mesh.
