Same here we lost our left elf charm in our shared world(1 save only). No way to reload old save files and sadly we weren't able to make the Sarah's Charm in the end due to this issue. From what we gather we think we lost it near the termite den due to a glitch spot. We somehow got stuck in the blue sheet cover climbing up and had to give up(die). When we went back to retrieve our backpacks, we notice some stuff were missing from inventory and backpack.
I do hope Obsidian allows one time only items(left elf charm, pinch whacker, badges, etc) to respawn after a certain amount of time if lost in the world or just don't make it one time items. Other than that though, I do love this game and do hope they fix this issue sometime in the future.