Partman crashed on install

[ben]

Trying to install Ubuntu 20... Groovy Gorilla LTS from USB on an older ASUS mobo (P5E3 Pro). Got to dialog asking how you want to install (e.g. Erase entire disk or "something else"). Chose Erase entire disk, confirm - yes. Got to timezone selection, then a message stating partman had crashed and to submit a bug report.

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: Sun Apr 25 15:05:02 2021
InstallCmdLine: file=/cdrom/preseed/xubuntu.seed initrd=/casper/initrd quiet splash --- maybe-ubiquity
LiveMediaBuild: Xubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
ProcEnviron:
 LANGUAGE=en_US.UTF-8
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 LC_NUMERIC=C.UTF-8
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)