The Problem

You can run into stability problems when running Proxmox VE on the HP Elitedesk 800 G4 Mini. For me these look like the machine randomly rebooting, usually daily.

The Solution

1. Edit /etc/default/grub
2. Change line GRUB_CMDLINE_LINUX_DEFAULT="quiet" to GRUB_CMDLINE_LINUX_DEFAULT="quiet i915.enable_dc=0"
3. Run sudo update-grub
4. Reboot

This will prevent issues with power management from causing the machine to reboot.

Thanks to this Proxmox forum thread for working out the issue.