Can you please tell which Antivirus software you are using ... ??
it's sound to me it's Norton, I'm not sure if you are using it.
I have got many case in my work same as yours, I uninstall it and shutdown issue resolved.
it has been known after reinstalling it again the problem fixed.
if you are using something els please let us know.
I have fixed many shuutdown issue at work.
Thanks