Openelec uses same system/storage partitions...I will try this....when you are in libreelec Live mode go to file manager in kodi and look for your openelec installation and rename it...In rpi I installed mini tool partition wizard on a windows PC and made a partition ext4 on hdd I boot to named hddstorage instead of storage as I had another storage elsewhere on the sd card then edit the cmdline...which is on the usb LE installation for Rpi....
so now my cmdline.txt looks like this" boot=/dev/mmcblk0p1 disk=LABEL=STORAGEHDD quiet"
I would try disconnecting ssd and try again..
Again I don't know for sure if you have the cmdline.txt in the nuc LE version..