Comment 5 for bug 1248320

Had the same issue in 18.04.1. From /var/log/dpkg.log this is what seems to be the relevant part:

2018-11-26 10:10:35 status half-configured grub-efi-amd64:amd64 2.02-2ubuntu8.9
2018-11-26 11:14:03 status installed grub-efi-amd64:amd64 2.02-2ubuntu8.9

I was doing something else when prompted about the conflict resolution, then (after about an hour, apparently) I clicked on "view diff" or similar, but nothing happened, the update just went forward.

Difference from the OP is that I don't remember having changed my GRUB config, so it's also a question why I was prompted in the first place.