It sounds like too much acidity was produce, pH got too low. That would account for the mozz-like stretchiness (pH of the curd got down to around 5.4), and the sticking of warm curd to the cheesecloth. Did you notice it took longer to get the vat to the usual/right temps? Or more or more active culture could have been used, thus presenting more starter bacteria producing more acid more quickly. By "brand new culture," do you just mean a new package of your usual type, or a new type/brand altogether? How was it measured - by volume (e.g. x teaspoon(s)) or by weight based on the dosage?