I noticed that my automatic crop farm using the farmer villager kept breaking because the farmer would not harvest any more. I tested this out in a survival world and I believe that they wont harvest unless they already have something in their inventory that they can replant. I believe that the reason my farm was breaking was because of the villagers new ability to actually use the composter which gets rid of their inventory and makes them unable to harvest. In the picture below it shows the test world where i gave the left villager a starter carrot and the right villager nothing.