Multi-Boot LibreELEC (HDD & USB)?

I have installed Plex Media Player to my computer's hdd. Plex leverages LibreELEC for their embedded PMP offering. This has been working great.

I also would like to occasionally use Kodi on this same computer. I figured I'd continue to boot PMP off the hdd and run Kodi on a USB drive as-needed.

Using two USB sticks, I installed LibreELEC w/ Kodi on one stick. When I pulled the "install" stick out and rebooted, the LibreELEC "Just enough for Kodi" splash screen displayed as it booted from USB (good). But then, instead of booting LE w/ Kodi, PMP started up. I can only guess that the LibreELEC on the USB noticed the LibreELEC on the hdd and ran that instead??

Any thoughts on how I can achieve this? I'd like to be able to use both Plex and Kodi independently on the same box if I can.

Thanks

Quote from nickr

At the simplest, enter the bios and choose to boot from usb or hard drive, depending which you want to use.

Thanks, I did attempt that. Even when I disabled the hdd from the boot options, it would boot off the USB (show the LibreELEC Kodi splash) and then proceed to load PMP off the hdd. I'll dig a bit deeper into the bios to see if there's anything I missed.

I really hoped going from PMP to Kodi would be as easy as popping the Kodi LibreELEC USB stick in and telling PMP to reboot.
[hr]

Quote from vpeter

I think you should manually set different volume labels at least on USB stick or use UUID in extlinux.cfg.

Interesting. Thanks, I'll take a look at that!

Edit: upon further searching based on the "extlinux" tip, I came across this thread which I believe would be applicable to my situation: LibreELEC I'll follow-up confirming if it works for me too.

Edit 2: Confirmed that this fixed things for me. On my hdd extlinux (this is PlexMediaPlayer /flash/extlinux.conf) I changed it to:
APPEND boot=/dev/sda1 disk=/dev/sda2 ssh quiet
and then on the USB stick (this is Kodi mounted while PMP is running: /var/media/System/extlinux.conf):
APPEND boot=/dev/sdc1 disk=/dev/sdc2 quiet ssh

This has allowed me to run Plex as my everyday system (hdd) and when I want to use Kodi, I plug in the USB stick and select reboot from the Plex menu. Similarly, if I am using Kodi and want to go back to Plex, I select reboot from the Kodi menu and pull the USB stick. Plex then boots up. Just what I wanted. Thanks again for the pointers!