My first farm was working fine (small farm with 3/3 workers assigned). When I created a second, larger farm, all farmers went to work on the clearing of the second farm and abandoned the first. Unlike with other build sites, I wasn’t able to reduce the number of farmers and since it wasn’t a farm yet, I couldn’t reduce the number of workers on it. Probably could have done this with the Professions window, but I figured I’d let the farm finish building.
Once it finished, all farmers are unable to work and/or idling. I do not yet have fences around my farms, so gates are not an issue. I followed the directions to update the local files.