CoreELEC has been installed onto eMMC using their "ceemmc" tool. CoreELEC runs just fine.
Device is now unable to boot Armbian from either SD card nor USB.
Can't restore stock firmware: Burn Card Maker throws an error when writing SD card. Also, manually created SD card gives a black screen.
It is clear written on ceemmc guide that the internal install need to be removed before a Android update is performed!