I had this issue since I've bought a new laptop (HP Pavilion 15 Gaming) with nvidia 960M. No matter which driver I use, properitary or nouveau with or without intel graphics turned on my machine won't complete reboot cycle or shutdown, it will just hang. This is with quiet splash turned on in grub config.
Without quiet splash it reboots and shuts down without a problem. I have tried numerous solutions with acpi options that I found on this site and others and none of it worked. The only thing that works is to remove quiet splash.
Does anyone have any insight why is this happening or how I can resolve this issue (remember all the acpi, acpi_* combinations failed for me) because it's been like this since day 1 from 17.04 onward.