If they still tast good, while spreading too thin, then you are overbeating the butter. Let the butter naturally soften to room temperature, Do not let it get liquidy. For me that is about an hour on the countertop at room temp.
When mixing the butter do not overbeat. Mix JUST until combined. After all the ingredients are in, refrigerate the dough for 1 hour. (My fridge is packed with onions, and other aromatics, so I cover my bowl with plastic wrap to avoid getting an onion smell in my cookies,
Overbeaten cookies will spread thin and crisp up. I use the Toll house bag recipe and my cookies get a nice puff to them and a soft chewyness to them