Mutable plugin and GASP are not working together. character’s breasts move upward and float around face level during gameplay

Development Character & Animation
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1

I’m using GASP 5.7 and replacing the default character with a custom one that has breast bones (2 additional bones). Without Mutable, everything works perfectly.

However, after adding the Mutable plugin and using the Customizable Skeletal Mesh Component, the character’s breasts move upward and float around face level during gameplay.

What’s strange is:

  • In the IK Retargeter, everything works correctly.
  • Without Mutable and without the Customizable Skeletal Mesh Component, everything also works correctly.
  • Physics does not seem to be the issue.
  • The breast bones are attached to Spine_4.

I can’t figure out where the problem comes from. Has anyone experienced something similar or knows what could cause this?