I have a fresh installation of Kubuntu 16.04.1 (kernel 4.13.0-32-generic). The home folder is encrypted (installation option).
My computer shuts down normally if the session is never suspended.
Nonetheless, if Kubuntu was suspended at some point, then the powering off does not work (only if
sudo poweroff -f is used). If powered off from the GUI the system seems to log off (log in screen appears).
If I do
sudo poweroff then I get:
Failed to start poweroff.target: Transaction is destructive. See system logs and 'systemctl status poweroff.target' for details.
It didn't use to happen on my previous Kubuntu 16.04.1 installation where the home folder was not encrypted.
My guess is that the suspending leaves some "information" behind that the system does not want to erase with the powering off. But it is a guess and I wouldn't know how to fix it.