I have the Sanyo Bread factory plus. Lately when I

I have the Sanyo Bread factory plus. Lately when I bake the bread in the machine the bread rises to the top and falls in the middle. I am useing the bread machine yeast and it's just purchased. I also use bread machine flour. I put the ingredients in the order give.This ws niver a problem but has now been for the last few times that I have made the banana bread. Do you have an answer for my Thanks. sylvia.