1) Has a full day passed? The game day tasks should update at 5 am.

2) Do you have a consistent, reliable connection to the Internet? In some cases, transient connectivity can cause a problem with day updates.

3) Have you manipulated your devices Date and Time in order to move the game along faster? This will cause disharmony in the game's internal clocks and the results are unpredictable (but not fun).

4) Do you play during the day (5 am to 8 pm) or does your day of game play start after 10 pm? Do you play between midnight and 5 am? There might be a problem with timing related to game play in the wee hours.

Those are a few of the problems I've had or have seen other people experience. My personal bugaboo is the connectivity thing; I trip on that one ALL the time. I suspect the most common reason is manipulation of the devices Date and Time.

In any case, report it to Support and they might be able to help you out.