if your butter was too soft the cookies will tend to flatten quite a bit. I find the best texture and spread happens with the butter is still rather firm, but you can put a finger print into it with a small effore and the butter should still feel somewhat cool.
My butter was room temp, not melting out of the paper wraper, when I opened the paper and turned the
butter out over the mixer bowl, it fell in with very little left on the paper. I keep those papers by the way to butter cake pans and such.
The cookies are very good, just flat. I wonder why it did not call for baking powder?