This will be because of one of two reasons; either the dough is too dry from not enough liquid (which won’t happen in this recipe - melted butter, dissolved sugar and pumpkin puree all help avoid this) or too much flour which will only happen if you scoop your cup into your flour to measure it out. The other reason would be that the dough is too cold. This is more likely to happen if you cook the dough from frozen if following the guides above. Also - the best way to avoid these issues and mistakes is to follow the accuracy rule - using digital scales to create the best cookie. It’ll be the best decision you make for baking in the kitchen!