I suspected this "could" be the culprit ever since I had the same issue a couple of weeks ago. I'm not sure if Intel is aware of it or if there is some kind of update/patch for it, but I will keep searching for one.
Do you also have Intel's Turbo memory?
I'm glad to hear your laptop shutdown!! Give me some kudos!!!
I've had this problem and the fix was uninstalling the "ThinkPad Power Manager Driver" from the Control Panel. Lenovo needs to fix whatever bug is causing the driver to hang the system on shutdown. Can you hear me Lenovo?