I have had this problem for a long time.
Im using the X96 Max+ with the sm1_s905x3_4g_1gbit dtb.
I have tried reinstalls, firmware flashes etc.
I cant seem to get to get coreelec to boot first and for some reason it only reboots to coreelec (with command reboot correelec) after about 10 minutes of being booted into android. Reboot update boots me to recovery and I can only boot to android then.
I think it’s problem because you boot coreelec from usb flash, I’m has same box and hasn’t that problem, but I booting CE from sd card or instal CE into nand.
Besides, for first boot CE after insert sd or usb into box , try to use android terminal and command:
$ reboot update
ore push the button in the a/v slot and provide power at the same time.
But I has problem long reboot to android, and I solving the problem via ssh from smartphone termius or any different console.
reboot to android: