I take it that you are using republic celebration for growth.
In order to celebrate a city, you have to have enough trade (after corruption) to produce enough luxuries to make half your citizens happy (and then use structures to make the rest content). This involves manipulating the placement of workers within cities, setting them to trade tiles (ocean, grassland road).
How do you define "two identical cities"? There are a several variables that affect happiness, so your cities are probably not identical.
You might have your celebration cancelled because it worked properly. When your city grows, the new citizen will be unhappy by default, so, if you don't monitor your cities every turn and make adjustments, the city will cancel celebration because of the new unhappy citizen. Hunger can be caused when the city has 1 surplus and there are no food producing squares for the new citizen to use.
Successful civilization play requires you to pay close attention to each city (eventually you will be able to solve most problems automatically), and this is especially true when trying to play republic or democracy. You have to alter production to suit your goals and needs; the computer defaults are NOT good advice (except by accident). You have to understand city mechanics. Use the "happy" button in the city status screen to see exactly how the happiness of your city is calculated.