Hi, I have been trying COREELEC dualboot to work on my Minix Neo U22-XJ for 2 weeks. Once installed, it worked without any problem, but when I went out to Android Minix, it did not appear again on restart, nor when I turned off the device. Until I have discovered that if I connect my hard drive with an adapter to the USB TYPE C input, the dualboot works perfectly, just like in the U1, that if I can only have that usb connection in addition to that of Coreelec. I have it connected by Land (etherner) and it's going great. The same you have already discovered or did not have the same problem but if not, I hope it will help someone.