Was/Is the version of android on your device 6.x? If so it sounds like a boot loader issue. I’ve had S905x boxes that would boot to CE 19.x but crash/reboot inexplicably.
The solution is to update to an Android 7.x or greater, either a general usage for S905x , ala Aidan’s Rom or ATVxperience or one of the other ROMS mentioned in the threads below:
https://discourse.coreelec.org/t/testers-wanted-gxl-1gb-ram-devices-amlogic-ng/15877/3
https://discourse.coreelec.org/t/s905x-1gb-android-6-and-coreelec-ng-boot-failure/14767
In a nutshell, do your reading as it’s all been covered in the linked threads. Please make sure you have a working ROM for your box before you try installing anything. That way you have something to fall back to if something goes wrong.