Shutdown and suspend buttons only logout

[Ragulan]

$ lsb_release -rd
Description: Ubuntu 18.04.1 LTS
Release: 18.04

xfce4-session:
  Installed: 4.12.1-3ubuntu3
  Candidate: 4.12.1-3ubuntu3
  Version table:
 *** 4.12.1-3ubuntu3 500
        500 http://gb.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        100 /var/lib/dpkg/status

When using the shutdown/suspend buttons in the whisker-menu, they only log the user out instead of shutting down or suspending the system. The issue started abruptly, but sometimes follows the expected behaviour.

Checking in dmesg shows this: [16654.247219] traps: xfsm-shutdown-h[15100] general protection ip:7fa72ec2298d sp:7ffe805e5cc0 error:0 in libc-2.27.so[7fa72eb8b000+1e7000]

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: xfce4-session 4.12.1-3ubuntu3
ProcVersionSignature: Ubuntu 4.18.0-13.14~18.04.1-generic 4.18.17
Uname: Linux 4.18.0-13-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CurrentDesktop: XFCE
Date: Wed Dec 26 19:40:43 2018
InstallationDate: Installed on 2018-12-21 (4 days ago)
InstallationMedia: Xubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
SourcePackage: xfce4-session
UpgradeStatus: No upgrade log present (probably fresh install)

[Theo Linkspfeifer (lastonestanding)]

This bug was reported on the Red Hat bug tracker too:

https://bugzilla.redhat.com/show_bug.cgi?id=1654568

[Theo Linkspfeifer (lastonestanding)]

Possibly a duplicate of bug 1703226.

Did you change any files which deal with power state permissions?

[Launchpad Janitor (janitor)]

[Expired for xfce4-session (Ubuntu) because there has been no activity for 60 days.]