We have an orphan lamb with a similar problem. He has always looked as if he's been disbudded, but now he has a third bald patch appeared on his head, plus the fleece along his spine is much (much) shorter than everywhere else. Originally I thought it was because he's quite dinky and has been known to climb through the fencing, and he was rubbing the fleece off. There isn't bare skin showing though, there is still fleece. However, when I fed him today I noticed it on his sides as well. We've looked really carefully and we can't see anything, just lack of fleece! On his head it's a bit scaly that's all we could see.