Installation Wizard crashing in Virtual Box on Win10

[snow]

I tried to install the Kubuntu 20.04 (dev branch) in VirtualBox on Windows 10.
When choose the language (German) and proceed then the installer crashes.
When I start again the crash happens again and again. So the problem can be reproduced.
I user VirtualBox 6.1.4 in Windows 10. My hardware is a new Lenovo Thinkpad 495.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubiquity 20.04.8
ProcVersionSignature: Ubuntu 5.4.0-21.25-generic 5.4.27
Uname: Linux 5.4.0-21-generic x86_64
ApportVersion: 2.20.11-0ubuntu21
Architecture: amd64
CasperVersion: 1.442
CurrentDesktop: KDE
Date: Wed Apr 1 00:09:41 2020
InstallCmdLine: file=/cdrom/preseed/kubuntu.seed maybe-ubiquity initrd=/casper/initrd quiet splash --- maybe-ubiquity
LiveMediaBuild: Kubuntu 20.04 LTS "Focal Fossa" - Beta amd64 (20200331)
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)