The cream cheese was not softened before mixing and/or was not thoroughly blended before adding the eggs.
The batter was overbeaten.
The oven temperature was too high. Check temperature with an oven thermometer.
The cheesecake was overbaked.
Doneness was checked with a knife or toothpick.
The cheesecake was cooled in a drafty area or the oven door was opened during baking.
Next time, try baking the cheesecake in a water bath.
You didn’t loosen the cheesecake from the sides of the pan with a knife while it was cooling.