As Japan, I just conquered all of China except the bit surrounded by Russian territory. It was way too easy in my opinion, though I don't know how to make China harder to invade without making it way too strong, but that's not why I'm making this post.

I decided to split China into four protectorate nations, to prevent any one of them growing too powerful, but this meant that the northern and western regions didn't have enough food, while the southern and eastern regions(and the Manchurian railway zone) had a surplus. So, the obvious thing to do is to transfer food from food-positive dependencies to food-negative dependencies, right? So I set up a food transfer deal between Manchuria and the North China Directorate, which works fine, but for some reason the deal between the eastern and western regions cancels after one turn, citing insufficient food supply! Even with the transfer, they've still got positive food production and more than 1k food in the stockpile, so why? (And no, I'm not accidentally trying to transfer food from the starving region to the fertile region)