I’d say grub is having trouble with your hardware (mainboard or disk maybe).
You could try to update your mainboard’s firmware, or install another bootloader (or maybe just a newer version of grub). I’m not sure what the easiest way to get a different bootloader is. I don’t think Debian’s installer offers anything besides grub. Maybe other people can point to a distro where installing something other than grub is easy.
Because switching out the bootloader on an unbootable system (i.e. not from the installer) is going to be whole pain in the butt involving booting into a live usb, mounting and chrooting and god knows what.