Metahuman Groom Issue With Mutable

General Issues and Bug Reporting
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Summary

Using the release branch of Unreal Engine source from github (at the time of writing this commit is dbd4567 on release branch),
I am using Metahuman Creator to create a basic metahuman with one hair groom. I use it with a basic mutable customizable object having body/face and the groom.
The metahuman hair is acting weird for low LODs (Mutable using cinematic metahuman has issues with LOD0-2, mutable using optimized metahuman has issues on LOD0 only)

Please select what you are reporting on:

Creative

What Type of Bug are you experiencing?

Assets

Steps to Reproduce

  1. Create an empty project add mutable and metahuman plugins.
  2. Create a metahuman that has hair groom added.
  3. Assemble a metahuman with cinematic option (or optimized option)
  4. Create a CustomizableObject and use the head skeletal mesh and the groom nodes to add the head mesh and the hair.
  5. Compile the customizable object

Expected Result

The head mesh and the hair should be added to the mutable output and hair should be attached to head properly.

Observed Result

The groom attached to head is distorted.

Platform(s)

Windows 11
Unreal Engine 5.7.2 (Source branch release and commit dbd4567 )

Upload an image

Optimized_Mutable_Groom_issue.png
Optimized_Mutable_Groom_issue.png901×607 644 KB

Cinematic_Mutable_Groom_issue.png
Cinematic_Mutable_Groom_issue.png1064×696 857 KB

Additional Notes

I created a minimal Unreal project that demonstrates the issue (the one used for screenshots)

2

I experimented a bit and found out that if I create the metahuman on Unreal 5.6.1 and migrate the head skeletal mesh to 5.7.1 (stable release), it works fine. (Using the groom that is exported by 5.7.1 too)

I assume it would work with the 5.7.2 release branch too.

So my guess is that the created mesh by Metahuman Creator after 5.7.1 is somehow different and breaks the binding for the groom component for low LODs.