EDIT: After further troubleshooting, and finding a typo in the preseed file, I can also confirm that the workaround proposed by @sclarkson is working successfully by allowing the installation to complete without error.
EDIT: After further troubleshooting, and finding a typo in the preseed file, I can also confirm that the workaround proposed by @sclarkson is working successfully by allowing the installation to complete without error.