I built a redstone factory full of automated farms. One of which depends on the farmer villager in order to be automated. At first, the villagers would farm but after a couple days the villagers would stop farming even after I spawned in a new farmer villager. It seems like all villagers just stopped working all of a sudden.
As soon as I spawn them in, they would just stare into nothing and freeze.
Yeah, villagers can only carry so much food before they lose interest. You need to lay down more farmland for them to plant more seeds and roots, and even then they will stop collecting wheat and beetroot sometimes once they have too much, because it's the crop and not the seed that determines when they have enough. You can also add more villagers by trading and adding doors, so the farmer caste members will donate some of their finished crops to them, allowing you to use the farm further.
Oh... Forgot to mention is that they won't harvest my farm full of wheat. I made farms for each individual crops so they won't get messed up. I also made a contraption that will kill the villagers and spawn in another farmer villager. They all seem to lose interest right away..
Killing villagers blocks them from breeding for a day but i don't know of it affecting whether they harvest or not. Are you sure your farm is fully villager-accessible? They can't open fence gates, trapdoors, use ladders or red-stone devices, or break crops that they are not directly on top of. (Even a tree overhanging a crop one block below will prevent that crop from being taken).