Unfortunately CoreELEC installed on emmc goes to compromise the Android bootloader, it would be helpful if there was a shell command to be able to reflash it without using reflashing methods that contemplate the use of MicroSD or crossed USB cables, since precisely CoreELEC compromises this possibility.
It would be enough or an option in CoreELEC’s power menu that would allow rebooting not only in bootloader that with multiboot put the tvbox in the Android recovery rather useless, but that it could actually boot from USB or MicroSD slot.