I'm not sure if this is the case, but it happened to me.

My pinstripe had to go through 2 sheds in order to figure out how to get the shed off his head. The humidity was perfect, he just didn't know how to quite go about it I'm guessing... The third shed he had was a complete one. So it might just take some time for him/her to get the hang of it. I've started misting the enclosure the night before I think they're going to shed though. Rather be safe than sorry.