I have a city, population 3, with 25/26 food, and 9-6=3 food per turn. Next turn it goes to 26/26 and stays there. I have tried loading from when it is at 25/26 and doing a few different things, but it always stops at 26/26 with no growth and says it is growing in 1 turn every turn. What are the potential causes?

You probably have the city governor set to "avoid growth"

I'd bet the farm on "avoid growth" too.

Or building a settler/worker?

As far as I know the only reason a city with the green circle/star, or "growth in one turn" won't grow is due to avoid growth.

ITs because you have no cows.

Can you put up a picture of that city screen?