Mac on High Sierra won't shutdown cleanly: black screen with mouse

Similar to issue "mac book pro sierra does not shutdown stays idle with a black screen and mouse".

Apple logo > Shutdown leads to black screen with mouse cursor. Stays like that for hours.

Realized this problem because it wouldn't install Mojave (also won't install 10.13.6 update). Seems I'm stuck on 10.13.3.

I tried verbose mode, but get the same black screen with no text on shutdown (did see lots of black screen with text on startup).

I get a bit more information when shutting down from Terminal:

$ sudo shutdown -r now
...
shutdown: / is busy updating; waiting for lock

Stays like that for hours. I used Activity Monitor to kill some random applications (starting with launchd) and it proceeds to shutdown. I narrowed it down to killing kextd to complete shutdown.

I've tried resetting PRAM. I've tried resetting SMC. I've tried removing everything from Login items (in Users & Groups).

Restarting in safe mode allowed proper shutdown:

Start your Mac, then immediately press and hold the Shift key. The Apple logo appears on your display.

Release the Shift key when you see the login window.

I was able to use safe mode used this to update to 10.13.6 (problem still existed) and 10.14 (problem resolved -- can now shutdown).

The same happened to me after upgrading to 10.14.6.

As referring to the answer here, I tried to shutdown with

sudo shutdown -h now

then terminal stuck with

shutdown: / is busy updating; waiting for lock

then I opened Activity Monitor and just force killed the process named kextd