[Solved] "won't shutdown" 101?

[Nodarkthings]

The forums are full of that issue, across the years and across the OSes — I'm facing it myself on 10.11 — with generally no answer at all or no convincing answer.
Isn't there someone here who could write a diagnose method or advices on what to check?
Seems like the Finder waits for something to happen but there's no activity and nothing really worthy in the Console...
- From what I read, might be fixed sometimes with FixShutdown option in clover.
- Some other say it's some app not succeeding being closed.
- Another one says it worked updating some kext.
- someone says to close the session first...

 

[Nodarkthings]

I finally found a fix! At least for my issue...
(I think the "won't shutdown" issue can have multiple causes, that's why there's no clear answer covering every possibility)
After countless trials, it appeared the Finder was not properly quitting but I was unable to relaunch it: my only option was to force quit identityserviced (or loginwindow from another account) in Activity Monitor, or to relaunch the Finder before attempting to logout.
And the Console showed a few lines of:
05/04/18 10:31:21,325 warmd[59]: [_bootcachectl_playlist_dir_for_user:2603] Assertion failed: (0 != uid): root playlist dir should no longer be used
and
05/04/18 10:31:21,394 WindowServer[199]: CGXGetConnectionProperty: Invalid connection 50211

Googling for the "warmd" message led me to a forum where, buried amongst the comments, someone wrote:
" If you use Avid products you might try removing:
/Library/Audio/Plug-Ins/HAL/Avid CoreAudio.plugin/
or
/Library/Audio/Plug-Ins/HAL/Digidesign CoreAudio.plugin/ "

An that indeed was my case!

So, my advice: if you face a similar issue, don't assume it's a hackintosh related issue, it might very well be a MacOS issue or third party app/extension. ;-)