Midonk That's unfortunate, sorry to hear. Does this issue only occur on a single skeleton asset? Or did you encounter this problem with multiple assets? If it only occurs at a single asset, you could try whether re-importing the respective skeleton asset directory perhaps resolves your issue. If re-importing does not fix it, you could delete the generated
SkeletonDataAsset, however be sure to first back-up the .meta file and then copy it back into the old location so that you don't lose any references to it. As usual, before deleting anything from your project, back up your whole project to be on the safe side.
Another standard way would be to delete the
Library directory and see whether this resolves any problematic incorrect state in the Unity project.