You can create a shutdown shortcut for full shutdown. Fast Start can cause incomplete shutdowns. Try turning that off in advanced power options and see if that makes a difference. I had this problem and had to also use the shutdown command shortcut for awhile but now the normal Shutdown actually turns off the computer completely. The error in Event Viewer is gone. Shutting Down Doesn’t Fully Shut Down Windows 10 (But Restarting Does) (howtogeek.com)    
In the Windows Reliability Monitor, I notice that almost every time I start the system, a "Windows was not properly shutdown" message is logged, and an "event 41 Kernel-Power Critical" & "event 6008 (previous system shutdown was unexpected) Error" pair is logged in the Windows System Log. There is no obviously abnormal thing happening each time I shut down Windows...but apparently this opinion is not shared by Windows and I guess there's an invisible crash happening nearly each time I shut down Windows ! How do I t'shoot something like that ? Could it be an old device driver ? I do have some legacy devices (but generally not connected) and "old" virtual device drivers (software), but trying to isolate the culprit by uninstalling them one-by-one seems a daunting task.
Windows doesn't shut down properly most of the time (Precision 5530)