I agree with Denny here.
As has been said, it really depends on you mashing regime, yeast viability/strain, fermentation health and recipe formulation to name a few. Using a calibrated hydrometer and thermometer are recommended here. I wouldn't rush to judgement on any one variable, but look a the big picture, then break down your process variables piece by piece. Start with your recipe first, then look at your mash schedule, then calibration steps, and so forth.