ubiquity crashed with ValueError in command(): invalid literal for int() with base 10: ''

Ubuntu Cinnamon Remix (https://github.com/Ubuntu-Cinnamon-Remix/iso-builder) Hirsute 21.04

Crashed after partitioning (when install began)

ProblemType: Crash
DistroRelease: Ubuntu 21.04
Package: ubiquity 21.04.1
ProcVersionSignature: Ubuntu 5.8.0-25.26-generic 5.8.14
Uname: Linux 5.8.0-25-generic x86_64
ApportVersion: 2.20.11-0ubuntu51
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.455
Date: Fri Nov 20 16:24:08 2020
ExecutablePath: /usr/lib/ubiquity/bin/ubiquity
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz boot=casper quiet splash ---
InterpreterPath: /usr/bin/python3.8
LiveMediaBuild: ubuntucinnamonremix "@BASECODENAME" (20201120)
ProcCmdline: /usr/bin/python3 /usr/lib/ubiquity/bin/ubiquity gtk_ui
ProcEnviron: Error: [Errno 13] Permission denied: 'environ'
Python3Details: /usr/bin/python3.8, Python 3.8.6, python3-minimal, 3.8.6-1
PythonArgs: ['/usr/lib/ubiquity/bin/ubiquity', 'gtk_ui']
PythonDetails: N/A
SourcePackage: ubiquity
Title: ubiquity crashed with ValueError in command(): invalid literal for int() with base 10: ''
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo