If you’re sure you used butter at the correct temperature, you may have accidentally ‘warmed’ your butter by mixing it with an electric mixer for too long.
Many cookie recipes start by creaming together the butter and sugar – this is just to combine the ingredients.
If you do this for too long, your room temperature butter will get super warm – and then you’ll face problem 1. all over again.
Some recipes depend on the dough being mixed just until the ingredients are combined, and not any longer. Other commenters are saying that overmixing cookies can warm the butter too much. With some recipes, like muffins, mixing creates gluten chains that lead to chewey-ness and toughness. So in order to avoid that you stop mixing asap.
Baking is a chemical reaction and the quantities, order, and methods really do have a huge impact on the result!