lubuntu 19.10 encrypt install bad unsquash configuration - filesystem.squashfs does not exist

sony vaio ultrabook (i5-9400u, 4gb, intel haswell-ULT)
Lubuntu QA-checklist install - full disk, ENCRYPTion, UEFI, NO internet

thumbdrive has been checked (check disc for defects) twice; once on d755-5 (prior live test) & once on this box

three tries (with reboots); they all ended with

`Installation failed. Bad unsquash configuration. The source filesystem "/cdrom/casper/filesystem.squashfs" does not exist`
(please note the above was typed, so it may not be letter perfect)

from logs
2019-10-09 - 10:33:16 [1]: ERROR: Installation failed:
2019-10-09 - 10:33:16 [6]: - message: "Bad unsquash configuration"
2019-10-09 - 10:33:16 [6]: - details: "The source filesystem \"/cdrom/casper/filesystem.squashfs\" does not exist"

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: calamares 3.2.12-0ubuntu1
ProcVersionSignature: Ubuntu 5.3.0-13.14-generic 5.3.0
Uname: Linux 5.3.0-13-generic x86_64
.etc.calamares.modules.finished.conf:
 ---
 restartNowMode: user-checked
 restartNowCommand: "systemctl -i reboot"
.etc.calamares.modules.partition.conf:
 efiSystemPartition: "/boot/efi"
 enableLuksAutomatedPartitioning: true
 userSwapChoices: none
 drawNestedPartitions: true
 defaultFileSystemType: "ext4"
.etc.calamares.modules.shellprocess_logs.conf:
 ---
 dontChroot: true
 timeout: 30
 script:
     - calamares-logs-helper @@ROOT@@
.etc.calamares.modules.unpackfs.conf:
 ---
 unpack:
     - source: "/cdrom/casper/filesystem.squashfs"
         sourcefs: "squashfs"
         destination: ""
ApportVersion: 2.20.11-0ubuntu7
Architecture: amd64
CurrentDesktop: LXQt
Date: Wed Oct 9 10:48:52 2019
RelatedPackageVersions:
 calamares-settings-ubuntu-common 1:19.10.6
 calamares-settings-lubuntu 1:19.10.6
 xfsprogs 5.0.0-1ubuntu1
 btrfs-progs 5.2.1-1ubuntu1
SourcePackage: calamares
UpgradeStatus: No upgrade log present (probably fresh install)