Yep, im working on this which will help give feedback to job failures in future, https://github.com/CleverRaven/Cataclysm-DDA/pull/37300
But in the meantime, heres the checklist.
- make sure the corpses are in a corpse loot zone, thats where the NPC searches for corpses.
- make sure the NPC has a butchering implement in their inventory or there is a loot zone with a butchering implement inside it nearby ( within 60 tiles )
- if the corpse is big, then they will also need a butchering rack, and a hacksaw.
- if its dark, then they cant do the task.
- as Valase also said - Im not entirely sure if the NPC can path on top of the rack, so might be worth putting the corpse loot zone adjacent to it.