I have been around the internet trying to find the answer and no solution given has worked.
I have disabled quiet and splash from /etc/default/grub so I can see the output. When shutting down, there are no errors, but the system halts on the line
[ OK ] Reached target Shutdown.
Does this mean the system has finished all processes etc.? After this I have to power down by holding the power button. This was also a problem in 14.04. Is there anything I can do to get the computer to power down?