Hallo,
is it posible to install new (beta) USB Raspberry 3 Bootloader for existing Libreelec instalation?
For my Raspbian and Raspbx it works perfect with scandisc usb stic.
Links:
1) How to boot from a USB Mass Storage Device on a Raspberry Pi 3 - Raspberry Pi Documentation
2) Pi 3 booting part I: USB mass storage boot beta - Raspberry Pi
Best Regards