/usr/bin/grub-probe: error: failed to get canonical path of `/'

I'm trying to install GRUB from a live USB onto a different drive. While grub-install works fine, grub-mkconfig -o /mnt/boot/grub/grub.cfg (/mnt being the mount-point of the drive I'm installing to) keeps returning an error:

/usr/bin/grub-probe: error: failed to get canonical path of `/'.

The advice I found online suggested running update-grub in a chroot might help, but the same error appears. My question is twofold: - How do I resolve this error? Seriously, I need to get this working - (more importantly) *Why* does this solution fix the issue? That second part is important because it would be useful for debugging if someone here explained the mechanics of what causes this issue, thus allowing more meaningful debugging in cases where the well-known solutions don't work. On the off chance that it's somehow meaningful to my issue, the system I'm installing from is a live ISO of Void Musl, and the system I'm installing to is Void Musl with / encrypted using LUKS, and encrypted /boot.