Hello, the warning is displayed when not all of the bones belonging to that constraint are in the skins that require them, or when the constraint is not in all the skins that would require it (this happens often when the constraint is in no skins at all, so supposedly always active, while the bones belonging to it are in skins).
You can expand a skin in the skin node to see what bones are in it. If something that should be there is missing, you found the culprit 😃
Skins - Spine User Guide: Skin bones
