Installing 18.04.3 from USB stick fails, unable to install grub

[Charles Halliday]

Final part of install of Ubuntu 18.04.3 from USB stick fails. Installation was replacing broken 18.04 on dual Windows/Ubuntu system.

uname -a (for installer) gives:
Linux ubuntu 5.0.0-23-generic #24~18.04.1-Ubuntu SMP Mon Jul 29 16:12:28 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

Tried to running grub install manually:

ubuntu@ubuntu:~$ sudo apt install grub-efi-amd64-signed
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 grub-efi-amd64-signed : Depends: grub-efi-amd64-bin (= 2.02+dfsg1-5ubuntu8) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

Installing boot-repair from yannubuntu/boot-repair and running it was enough to make a bootable installation, but I don't know if anything else is missing from the install.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.14.12
ProcVersionSignature: Ubuntu 5.0.0-23.24~18.04.1-generic 5.0.15
Uname: Linux 5.0.0-23-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.7
Architecture: amd64
CasperVersion: 1.394
Date: Sun Dec 15 21:18:11 2019
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash ---
LiveMediaBuild: Ubuntu 18.04.3 LTS "Bionic Beaver" - Release amd64 (20190805)
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)