Booting NetBSD 8 install image on PC Engines apu2d4 via serial console goes blank

["J. Lewis Muir" <jlmuir%imca-cat.org@localhost>]

I'm trying to install NetBSD 8 on a PC Engines apu2d4

  https://www.pcengines.ch/apu2d4.htm

via a USB thumb drive with a NetBSD 8 install image

  https://cdn.netbsd.org/pub/NetBSD/NetBSD-8.0/images/NetBSD-8.0-amd64-install.img.gz

via a serial console where I can get to the welcome screen of the
installer image

  Welcome to the NetBSD/amd64 8.0 installation image
  ===============================================================================

  ACPI (Advanced Configuration and Power Interface) should work on all modern
  and legacy hardware.  However if you do encounter a problem while booting,
  try disabling it and report a bug at http://www.NetBSD.org/.

       1. Install NetBSD
       2. Install NetBSD (no ACPI)
       3. Install NetBSD (no ACPI, no SMP)
       4. Drop to boot prompt

  Choose an option; RETURN for default; SPACE to stop countdown.
  Option 1 will be chosen in 0 seconds.

  Option: [1]:

and I press Space and then Enter to start the install, and it shows
some numbers with a spinner and then shows

  18010904+813996+1283156 [1191264+821120+12847-

 but then the screen goes blank.

Does anyone know what I can try to get this to work?

I tried the "no ACPI" and "no ACPI, no SMP" install choices, but that
didn't help.

The apu2d4 says the serial port baud rate is 115200 which is what I
successfully used to communicate with the apu2d4.  Will the boot image
kernel work with this baud rate?  If not, is there a way to change it
by dropping to the boot prompt?  Or do I need to build a custom kernel
with the baud rate set to 115200?

Thank you!

Lewis