Why doesn't my Ubuntu kickstart work?

Question

this is my first attempt at any kind of unattended install. I have a VirtualBox machine with the Ubuntu 18.04 desktop ISO attached. After starting up:

• I hold down the left shift key, then hit enter for English
• I arrow down to select Install Ubuntu
• I hit F6 Other Options, then Escape
• I type the following and then hit enter: auto=true ks=https://path/to/my/ksfile.cfg
• From here it proceeds to the regular graphical installation, ignoring my kickstart file, and giving me no indication of what went wrong (or maybe I don't know where to look).

To test networking: I appended a 3 to the end of the boot parameters, got to a console, ran ifconfig and ping and confirmed everything was up. I also put the interface name I found there explicitly in the kickstart file, changing it from network --bootproto=dhcp --device=auto to network --bootproto=dhcp --device=enp0s3 -- this didn't help either.

I'm using a simplified version of the kickstart file here, with no preseed: https://github.com/vrillusions/ubuntu-kickstart/blob/master/18.04/ks-1804-minimalvm.cfg I have also tried generating one with system-config-kickstart and that didn't work either, so I doubt it's a problem with the file itself.

Questions:

• Anything obvious I'm doing wrong?
• Is there something that would help me troubleshoot the error?