There may be many reasons, such as yeast failure, less yeast, too low water temperature and the failure of the bread maker itself.

My own experience, if the above is normal, if you think the dough is not fermented well before baking, you can cancel the operation and extend the fermentation time of the dough. After an hour, watch the dough start, and then bake it separately according to the baking function to ensure that it will rise every time.