Booting to Android Recovery or TWRP Recovery sometime may be enough to stop LibreELEC from Autobooting again when you power on or reboot from Android.
In that case simply hold in the Reset button again, or whatever method you first used - when connecting power to restart autobooting into LibreELEC.
I performed the reboot process a couple of times going from LE to Android and back again and it will keep going back to LE automatically now indeed. I'm 100% sure that I had to perform the reset button method again in the past to get back to LE, so there must have been some instability in LE builds and/or Android booting at the time.