I had to flash first Armbian, and then in their config script do this:
armbian-config —> System → Install → Install/Update the bootloader on SPI/Flash
Original thread: https://forum.armbian.com/topic/19340-odroid-c4-will-not-reboot-after-any-sort-of-kernel-update-have-tried-running-nand-sata-install/#comment-137689