I do have the latest. I think it's a new bug. I was just able to keep playing past a farm creation in another save.
When the bug occurred, the farm I built slightly overlapped the water on a pond. I believe the bug emerged due to a rendering conflict between the two. Or something similar perhaps?
Hmm sound like a strange bug. Most slowdown occurs because of pathfinding (such as trying to go somewhere you can't reach). Might be that a farmer tried to farm at a spot within the field that was unreachable for some reason. Thanks for the report, put it on my to-do list!