If a jobless villager is approaching a jobsite, which is standing on a lower Y level than the villager is walking on and the top of the jobsite is blocked off, then the villager will stop at the ledge if it is no more than 1 block away from the jobsite block and just stare at it and never aquire the profession.
It will stand here indefinetly untill it is either pushed towards the jobsite or the block on top of the jobsite is removed. Even ignoring nightfall despite it having a bed.

See this screenshot for clarification of the placement of the jobsite block in relation to the ledge and where the villager approaces from (its a bit difficult to explain in text)

Is related to MC-186314