Cacio e Pepe problems, diagnosed

First check when the cheese failed. If Pecorino turned into rubbery or stringy knots as soon as it met the pasta, the mixture was usually too hot for its starch and water balance. If the sauce started smooth but then loosened or separated, the water phase may not have contained enough starch to keep the cheese dispersed. A coarse, dry cheese paste or aggressive reheating can create different versions of the same failure.