Changing the Virtualbox settings and the kernel command line to output to a text file on the host machine (see https://www.virtualbox.org/wiki/Serial_redirect) worked to get a log file, but caused the "Please remove the installation medium, then press ENTER:" screen as well as a text-mode animation to show up. Pressing enter did not cause the system to shut itself down though. The text-mode shutdown animation continued to display along with the "Please remove the installation medium, then press ENTER:" message. Due to the fact that the issue changes whenever logging is set up, it will likely be difficult to debug this issue fully.
Changing the Virtualbox settings and the kernel command line to output to a text file on the host machine (see https:/ /www.virtualbox .org/wiki/ Serial_ redirect) worked to get a log file, but caused the "Please remove the installation medium, then press ENTER:" screen as well as a text-mode animation to show up. Pressing enter did not cause the system to shut itself down though. The text-mode shutdown animation continued to display along with the "Please remove the installation medium, then press ENTER:" message. Due to the fact that the issue changes whenever logging is set up, it will likely be difficult to debug this issue fully.