unable to install grub with Win10 dual boot

[Damien Danneels]

I am installing Ubuntu 19.10 on my new computer, keeping Windows 10 as dual-boot. I've previously disabled secure-boot and settled legagy boot instead of UEFI.
I've manually partitioned my free disk space with LVM and an EXT4 root partition. At the end of the installation process, i get an error when trying to write the boot loader (grub-install). I've tried both whole disk device and first partition (EFI system, already installed with Windows).

While still running from installation usb key, i tried to manually run "sudo grub-install /dev/nvme0n1p1" which gives something like "unable to obtain canonical path to /cow".

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: ubiquity 19.10.21
ProcVersionSignature: Ubuntu 5.3.0-18.19-generic 5.3.1
Uname: Linux 5.3.0-18-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu8
Architecture: amd64
CasperVersion: 1.427
Date: Thu Oct 17 23:20:50 2019
InstallCmdLine: file=/cdrom/preseed/ubuntu.seed only-ubiquity initrd=/casper/initrd quiet splash --- debian-installer/language=fr keyboard-configuration/layoutcode?=fr keyboard-configuration/variantcode?=oss
LiveMediaBuild: Ubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)