Does your trench coat mesh have additional bones by any chance?
I am having a similar problem in 4.10 and 4.11 preview. In my case, the slave component’s skeletal mesh has additional bones. The extra joints seem to translate to a location near the root bone when in play or in simulation in editor - with or without an animation applied to the character BP. The result is the slave component’s mesh stretching towards the floor like in your picture.
The skeletal mesh for the slave component was FBX imported to share the master component’s skeleton without any error. When looking at the individual meshes in the Persona editor, applying an animation to the skeleton and switching between the master and slave meshes for preview, I don’t see any apparent problem there.
I haven’t encountered this problem when using meshes without additional bones for the slave component.