For me, a similar thing has happened whenever during an update grub was updated, unless I enter following two lines into the terminal after the update and before rebooting:
sudo grub-install [...]
sudo grub-mkconfig -o /boot/grub/grub.cfg
whereby [...] needs to be replaced by the right command for BIOS or UEFI.
See this forum topic: Attention grub update.
Maybe that’s what can prevent you from having to archroot.