A clean flashed eMMC module, after boot, did
sudo apt-get update
sudo apt-get upgrade
sudo reboot now
Rock 5B would reboot, display flash screen, then nothing but a flashing cursor. - Hung
Re-flashed eMMC module, after boot, did
sudo apt-get update
sudo reboot now
Rock 5B would reboot, display flash screen, then show login screen. - Normal operation
I tried multiple times, always the same behavior.