ubiquity fails on grub on custom patitioning with boot and efi on separate microsd

[Madalin Ignisca]

I'm trying a more particular partitioning scheme and every time ubiquity fails to finish the grub install.

I have 2 nvme drives, identical, formatted full disk with btrfs in raid0 to make my rootfs.
Additionally, for boot (ext4) and efi partitions, a separate microsd card.

Before finishing, ubiquity shouts a failure and looking in I can see that grub failed to install.

I managed to do this particular partitioning scheme using Arch Linux, and installing grub as per the wiki worked without any error or warning. I can't understand why there is something opinionated in Ubuntu's installer that would fail grub installation.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubiquity 20.04.15.2
ProcVersionSignature: Ubuntu 5.4.0-42.46-generic 5.4.44
Uname: Linux 5.4.0-42-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu27.4
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.445.1
Date: Mon Nov 30 06:42:16 2020
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 LANG=ro_RO.UTF-8
 SHELL=/bin/bash
 LC_NUMERIC=C.UTF-8
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)