Critical crash while initial install of Kubuntu 20.10 at the step or grub install

[Sébastien D'Amboise]

I have 2 hard drivdes, sda has Windows 10 and sdb has multiple partitions with test distributions of Linux. When installing Kubuntu from a USB stick, the process fails close to the end when grub2 is ready to write to the mbr. Then installer exits. Repeated the process many times with same results. Ensured no proprietary driver was loaded initially.

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: ubiquity 20.10.13 [modified: lib/partman/automatically_partition/question]
ProcVersionSignature: Ubuntu 5.8.0-25.26-generic 5.8.14
Uname: Linux 5.8.0-25-generic x86_64
ApportVersion: 2.20.11-0ubuntu50
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.455
CurrentDesktop: KDE
Date: Fri Mar 5 10:35:27 2021
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/kubuntu.seed maybe-ubiquity quiet splash ---
LiveMediaBuild: Kubuntu 20.10 "Groovy Gorilla" - Release amd64 (20201022)
RebootRequiredPkgs: linux-image-5.8.0-25-generic
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)