Hi: If the diaphragm is fine. It may be a lack of water pressure at the exit of the appliance. Try to clean the shower flower. Sometimes the perforations of the rain are blocked and that fault occurs, if that is fine and the problem continues, it may be that the serpentine is partially covered. at first sight because less water comes out with less pressure to solve it uncover the serpentine with muriatic acid lowered with 50% water