I have seen this a few times but it is fairly rare. I capture a city and go to the build screen to see what the city needs. For example, in my current game in one city the only building I can build is Harbor. So I think that all the other buildings have been build. But when I go to the detail screen, the only improvement there is Fortress. I then rush built the Harbor and the next turn the only building in the menu is Watermill. The city is not land-locked, there is room for expansion. Unrest is at 75% but I am not seeing the *no production* message. Looking at my other cities, they all include the option to build Iron Works or Hosten's Library but this one does not.