I used the Aug 23 preview ISO for KDE Neon Bionic to install Neon to my PC. I have my laptop docked with the lid closed. When I attempt to shut down from Plasma or log out and end the session, the laptop goes immediately to suspend. This does not occur if the laptop lid is raised first. Changing options related to suspend in the Power Management settings did not help. As a workaround, I modified /etc/systemd/logind.conf to ignore the laptop lid switch, like so: HandleLidSwitch=ignore It now shuts down and logs out properly without suspending. This issue has only occurred with Neon. Linux Mint and stock Ubuntu do not exhibit this behavior. Neon should ideally have systemd configured to ignore the laptop lid being closed in case it is docked.
Update: I installed Mint Xfce, and replaced Xfce with KDE (from Kubuntu). At first everything was working fine...until I installed the latest Nvidia drivers from the Ubuntu Graphics PPA. Only then was I able to replicate this problem. As such, this appears to be an issue with Bionic in general, combined with the Nvidia driver, and is not specific to Neon. I'll file a bug report with Canonical shortly.
Thanks for the update; changing status. You could add the link to the Ubuntu ticket here.