Some background jobs saturated CPUs to > 200% just before the shutdown happened:
You can list scheduled tasks with sudo systemctl list-timers and sudo crontab -l and see if the culprit can be found by its execution schedule. You can also look at the system logs around the shutdown time, background processes usually leave some trace.
You can somewhat harden klipper against disruption by background tasks by adding to /etc/systemd/system/klipper.service:
[Service]
Nice=-18
IOSchedulingPriority=1
But in general, I recommend not running the Klipper host on a desktop linux distribution, since they often come with lots of fluff running automated background updates, checks, backups, etc.