package grub-pc 2.02+dfsg1-12ubuntu3 failed to install/upgrade: installed grub-pc package post-installation script subprocess returned error exit status 1

during do-release-upgrade --devel from disco. base system was a raid 1 btrfs on two drives.

ProblemType: Package
DistroRelease: Ubuntu 19.10
Package: grub-pc 2.02+dfsg1-12ubuntu3
ProcVersionSignature: Ubuntu 5.0.0-20.21-generic 5.0.8
Uname: Linux 5.0.0-20-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu3
Architecture: amd64
Date: Thu Jul 11 21:24:56 2019
ErrorMessage: installed grub-pc package post-installation script subprocess returned error exit status 1
InstallationDate: Installed on 2018-11-04 (249 days ago)
InstallationMedia: Lubuntu 18.10 "Cosmic Cuttlefish" - Release amd64 (20181017.2)
ProcCmdLine: BOOT_IMAGE=/@/boot/vmlinuz-5.0.0-20-generic root=UUID=52b46f84-d504-4f35-95d5-f9c73ed3d001 ro rootflags=subvol=@ resume=UUID=5408cfaa-8e4c-45b3-8b4e-971b0196043c
Python3Details: /usr/bin/python3.7, Python 3.7.4rc2, python3-minimal, 3.7.3-1
PythonDetails: /usr/bin/python2.7, Python 2.7.16, python-minimal, 2.7.16-1
RelatedPackageVersions:
 dpkg 1.19.6ubuntu1
 apt 1.9.1
SourcePackage: grub2
Title: package grub-pc 2.02+dfsg1-12ubuntu3 failed to install/upgrade: installed grub-pc package post-installation script subprocess returned error exit status 1
UpgradeStatus: Upgraded to eoan on 2019-07-12 (0 days ago)