Ubiquity consistently crashes in Ubuntu 20.04

[PJSingh5000]

It's not clear what the bug or issue is.
Attempting to install Ubuntu 20.04 on HP Spectre.

The only message I see on the command line is...
$ ubiquity
/usr/bin/ubiquity:74: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
  import imp

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubiquity 20.04.15
ProcVersionSignature: Ubuntu 5.4.0-31.35-generic 5.4.34
Uname: Linux 5.4.0-31-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.445
Date: Fri May 22 23:23:08 2020
InstallCmdLine: BOOT_IMAGE=(loop)/casper/vmlinuz boot=casper acpi=off iso-scan/filename=/ubuntu.iso noprompt noeject
LiveMediaBuild: Ubuntu 20.04.0 2020.05.23 LTS "Custom Focal Fossa" (20200522)
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)

[PJSingh5000 (pjsingh5000)]

Ubiquity crashes when installation is almost finished.

[PJSingh5000 (pjsingh5000)]

When I try to re-run ubiquity, I get the error, ubi-partman failed with exit code 10.

[Cubic PPA (cubic-wizard)]

The issue was because the customized filesystem.squashfs was missing the /proc and /tmp directories.
Ubiquity expects these directories to be present, because they are not automatically created during the installation process.
Including empty /proc and /tmp (and /run) directories solved the problem.