2-3 years ago, an update to GRUB completely fucked the bootloader on Arch systems. I remember it well because it was the only time I was thankful for choosing Manjaro (which receives updates on a delayed schedule).

(edit) Found it! https://archlinux.org/news/grub-bootloader-upgrade-and-configuration-incompatibilities/ A breaking change in the GRUB configuration caused systems to become unbootable. Manual intervention was required to regenerate the config files (I think it was supposed to be handled by a pacman hook but can’t be sure).