![Image](https://i.ibb.co/d7rhCr0/Farm-Extend.png)
You can extend it if you remove the zoning:
![Image](https://i.ibb.co/K0S12MF/Farm-Extend-No-Zone.png)
In addition I have this problem after I saved the game and tried to extend the farmland (this occurred after I found the problem and tried to provide a save game, I don't know how related the issue is):
![Image](https://i.ibb.co/GnXGtKz/Farm-Extend-Error.png)
Note: This error ONLY happens if you open the game and immediately load the file. If you start another game and try to load that file that error stops happening for some reason.