I believe this is a UI bug. I've had this happen to me where it says city growth stagnant and food required to grow is 0 like in your example. In my case, the food required to grow was actually some number slightly above 0, say 0.01. So the city grew the following turn.
It definitely makes planning harder when you're counting on a city growing in 1 turn only to find out the following turn its turns to growth is now 0 so that it was actually two turns away.