If you are no longer using a layer I would recommend deleting it to improve the efficiency - the program will continue to process layers even if they are hidden. I'm sorry that I cannot figure out why that layer is not appearing in the scene. It's possible that the program has placed the object far away from the rest of the puppet and it just needs to be dragged into place, but I doubt it. It might just be the best use of your time to re-import the puppet and rig it again.
Sorted. I retrieved the whole project from the external storage and its all working, apart from a lost link to an audio file which comes from the Character Animator Example Assets folder which I cannot find. Lost when the files were copied from the original external storage to the network location (please don't scream - I know that was a bad move but had no option).