I had similar trouble, not able to see the device or ssh despite being able to ping and see DHCP discover requests from it in wireshark. Setting fixed IP address also did not work. The problem was it was booting in emergency mode, so any attempts to connect with the RJ45 were not working. Only screen-ing in over usb-c in the console port, login, reboot, and press control-D after the notice of emergency mode could I make any progress and it has been smooth since.
