For mine also same notification was coming. I turned off windows defender due another security QHTS. Now, not appearing the notification. But, one problem still going on,, after shutdown the windows Laptop's keyboard light continues on too many long times.
One or more third party application is interfering with Windows 10, that's why they are not letting windows to shut down.
You have to use trial and error method to find which application is causing this issue.
steps :
1. Open task manager and select startup tab. Then disable all except important ones like display drivers(like Nvidia/AMD related), touchpad related(like synaptic/Elan touchpad application) and sound card(like realtek/conexant related) etc.
2. Then restart and check the issue.
If it doesn't exists then enable few more(not all just 3-4 so that you can be sure which app is causing the issue) and remember them and restart. Check the issue. Follow this steps again again to find out the app. This way you can be sure which app is causing this issue :k