LM repair will only work if a pick has taken a modest amount of bends since its last repair, if you bend it a lot of times before it breaks, you can't use LM repair and have to go to the NPC.

If you assess the pick after each bend, you'll see the "condition" gets worse, and LM repair doesn't work once the condition gets bad enough.

This isn't new, but you have to be pretty lucky on damage rolls to get enough bends prior to the break to be hit by it, so you can play a long time before you first see it. I'd probably used LM repair a hundred times before I first saw it.

People used to just throw picks away when it happened, but the NPC will repair it, and it will be repairable by you in future provided it doesn't lose too much condition before it breaks again.

Its a tricky thing to research so I've never actually worked out the exact condition where LM repair stops working, but I've only ever had this happen with picks in really bad condition.