I am using Ubuntu 16.04 with the latest 4.7.x kernel from mainline repositories (due to this amdgpu bug in the default kernel version) and my system is not shutting down after some hours running. The same problem is happening in the latest version of the 4.4.x kernel available for this release of Ubuntu.
The console shows that systemd had turned off the system successfully but Plymouth is still up on my screen until I force the shutdown via the button. I've already tried to boot up using acpi=force and acpi=force apm=power_off but none of these parameters fixed that issue..
Someone knows how to fix it?