Guto Unfortunately, I am not sure your situation since the mp4 you attached does not play correctly. However, the issue you described likely occurs when that bone is bound to a mesh attachment that is also present in other skins. In such cases, if the bone isn't active when that mesh attachment is active, the mesh vertex positions cannot be calculated correctly. To prevent this issue, Spine automatically adds the bone to other skins that require it.
For your information, if a bone bound to a mesh attachment cannot be referenced—such as when it is not included in the same skin—a warning symbol will appear in the tree view:
For more details, please refer to the following section in the user guide:
Spine用户指南 皮肤 #警告
