Last night I ran "pacman -Syu" to update my system for fixing the xz backdoor vulnerability.

Mid-update, everything froze so I reached out to power button to reboot. That was a mistake.

When I rebooted, my bootloader was GONE. I had to boot from a live ISO to reinstall the bootloader. 

 At what point did it freeze? Was it OOM? What bootloader do you use? Do you use secure boot?