installer crashed during installation on an iMac, even though I used it many times to install Lubuntu on PC laptops

[Owen Peery]

I used a bootable USB drive to try to install Lubuntu on an iMac from 2011. It crashed during the final phase of installation. I have used the USB drive many times to install Lubuntu on old PC laptops and it worked fine. Not sure why it crashed on the Mac.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.14.6
ProcVersionSignature: Ubuntu 4.15.0-29.31-generic 4.15.18
Uname: Linux 4.15.0-29-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CasperVersion: 1.394
Date: Fri Nov 2 17:12:39 2018
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/lubuntu.seed boot=casper only-ubiquity quiet splash ---
LiveMediaBuild: Lubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
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: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)