As part of my trying to get my Solitude working in this thread, I also did a firmware upgrade.
With the latest firmware a reboot with a USB kbd plugged in almost always ends up showing that eMMC is not detected, Card did not respond to voltage select! -110v.
Unplugging the USB kbd and replugging the power supply makes eMMC boot just fine.
This was not an issue with the stock firmware that came on the Solitude.