Help with YO YO loach

[Jimmy120883]

What is happening with one of my YOYOs?
It's happened before a few months ago but not as bad and sorted it's self but I'm not sure what's happening.
Is it stress? An infection or somthingn YOYOs do from time to time.

 

[Magnum Man]

doesn't look like it's something that it will just get over... also doesn't look like a YoYo