Comment 23 for bug 1896608

installed grub2 2.02-2ubuntu8.18 and configured debconf & /boot to reproduce the issue (touched the core.img, as well as enxsured that install_devices_empty & install_devices are marked as seen, and set to true and empty respectively).

dpkg-reconfigure -u grub-pc exits zero as expected.

upgraded to 2.04-2ubuntu8.19, and executed dpkg-reconfigure -u grub-pc again, and it is also successful.

bionic-updates didn't have the "exit 1" bug, and it still is not there with latest round of fixes from focal.