Have you disabled the "auto-share external drives" option in Settings\Libreelec\Services?
I'm not sure on other consequences of turning that off. Nor if it will work in your scenario. I mention this because if this disables a share you have to be careful when updating the library in case you accidentally say yes to remove library items for a no longer existing source path.
A backup might be prudent.
Thanks for your reply. It should work, thank you.
However, why should I create a backup? Removing all library items (on the client) won't remove actual disk files on the Samba server, right? You're scaring me a little bit here 
No, you won't loose the source files. But large libraries can take time to re-scrape, which might anger some people. Plus others have custom NFO files for artwork and things that might get screwed up, which might anger some people.
It's not a comment on you. Just a bit of CYA. 
