The Bone exists only on the skeleton but not on the current mesh.

So here is a picture with the default mannequin:

And this is what I get when I try to change skeletal meshes.

Hi, I have same problem. Its uppear when you try to reimport you skeleton with new bones (added in 3d software). And here my decision.

  1. Create new project whith same hierarhy of folders (from content to you skeleton).
  2. import in this project new skeleton whith changed or added new bones
  3. migrate skeleton asset to you primary project. if folder path are same - you got updated skeleton whithout this gray bones.
    if you know another speed way, tell pls.

Thank you Eugine. That solution actually worked!

@Hunanbean I am not familiar with that method. Is there a way to elaborate further on the steps and dumb it down for me? I’m newer but not new to Unreal Engine and this is a common issue I am finding.

@nostringz I do not think i could explain it any differently… I just followed his steps