Whoops, in my haste to add the warning, I forgot some potentially useful debugging information...
The systems that work have grub-pc/install_devices set to a path under /dev/disk/by-id. On the systems that don't work, the /dev/disk/by-id directory doesn't contain anything for the hard drive. One has a USB drive only; the rest have no /dev/disk/by-id directory at all.
Whoops, in my haste to add the warning, I forgot some potentially useful debugging information...
The systems that work have grub-pc/ install_ devices set to a path under /dev/disk/by-id. On the systems that don't work, the /dev/disk/by-id directory doesn't contain anything for the hard drive. One has a USB drive only; the rest have no /dev/disk/by-id directory at all.