Coreelec are using an outdated and not compatible with other new systems technology run from external media. No matter what you have in eMMC. If you are running coreelec from external media, then your eMMC has an old version of multi-boot that is not compatible with the new systems. No new system can run properly on your device anymore.
So actually in order to launch LE from the Amlogic boxes, I need to update the internal Uboot first?