If I leave the computed idle for a long amount of time when I try to shutdown using the options from the top bar nothing happens. As a work-around, I can log out first and then use the shutdown in the greeter top right-hand corner. Otherwise, shutdown from the terminal also works.
Grub options are as follows:
GRUB_CMDLINE_LINUX_DEFAULT="quiet acpi=force reboot=acpi"
In /var/log/syslog I see this error:
wingpanel: EndSessionDialog.vala:112: Unable to reboot: GDBus.Error:org.freedesktop.DBus.Error.InteractiveAuthorizationRequired: Interactive authentication required.