Actually found the solution on the forums, worked for me:
Hey guys! I found a better workaround than splitting the body and head meshes. Here are the steps:
Drop your mesh and hair into the scene, attach the hair to the mesh.
In the content browser, right-click on your imported skeletal mesh → create a new physics asset.
In the Phat editor, delete all the physics bodies but the one for the head.
In the skeletal mesh editor under “Physics”, assign the newly created physics asset. (If it doesn’t update, toggle between old and new. The preview icon in the content browser should focus on the head now.)
Create a groom binding asset for your hair and select the skeletal mesh under target mesh.