Which version of CoreELEC did you try to install?
Entirely possible that it’s related to an issue with an incompatible version of Android, more specifically its bootloader. What Version of Android is currently installed on the box? If it is a version less than 7.1 you’ll need to upgrade the Android to make use of the bootloader to be able to boot CE NG versions.
If this is the case, this has been covered extensively in these forums. Here’s a link to a good place to start looking for info on the subject:
https://discourse.coreelec.org/t/testers-wanted-gxl-1gb-ram-devices-amlogic-ng/15877/4?u=kshi