I'm not sure what would have caused that, though mal-nutrition comes to mind first considering the species and their dietary needs. I'm not sure what you would do about this at all.
i just fed them a large star (i feed them every 2 wks) and they immediately went for it, so at least i know it still has an appetite... will cross my fingers
It will come back after a molt or two. It could have been physical damage from a number of causes or it could have been a bad molt. Either way it will regrow.
I had one that was missing a claw that I got from a club member when he was breaking down his system. His claw grew back with the next molt. I think that you should be fine.