I thought they were supposed to occur at a rate of once per day (once per real day, not Isola day ). Although they don't "stack" - so if you don't open your game for a few days, you only get one event.

Have you reset your system clock recently - either deliberately (to make the game go faster) or accidentally? This can mess up the game's internal timing - I think not getting events is one of the problems that changing the system clock causes.