I have an X96 pro plus with coreelec on SD card.
Sometimes (specially when I unplug and plug the power cable) the box boots with Android and not with coreelec.
It is random and sometimes I solve it restarting the box, sometimes I have to remove and insert again the SD.
Any suggestion on how to solve this problem?
You could see if the problem persists with another SD Card.
Some boxes seem a little finnicky with regard to power demands on the USB ports. I have an older X96 box which reverts to booting in Android if there are multiple devices on the USB ports eg. a hub with mouse and keyboard and/or certain USB sticks of an older generation. Try booting with nothing plugged in the USB ports.