MAPE can be a problem also if you have a problem where rare excursions are what you want to predict and the cost of missing an event is much higher than predict

MAPE can be a problem also if you have a problem where rare excursions are what you want to predict and the cost of missing an event is much higher than predicting a non-event. A model that just predicts no change would have very low MAPE because most of the time nothing happens. When the event happens, however, the error of predicting status quo ante is much worse than small baseline errors.