[shiro]

If you have your Kodi's libraries builded and the script.skin.helper.service addon properly installed then it should work fine...

Well, even after skin reinstall and soft reset of LibreElec (complete wipe of all settings, addons, etc., LibreElec OS and its Kodi 17.3 is completely clean like its first run after install), it still not works.
I will check that script.skin.helper.service addon, and try to reinstall it if something is weird. UPDATE: addon is OK and properly installed on HTPC and the other PC I mentioned below.
I have indexed my video files into libraries like I do everytime: Set Content -> I choose folder which contains movies -> movies are in directory which match file name -> click OK and it begin to index, download info and artwork.

And to be complete...it does not work also with clean install of Kodi 17.3 on my other PC, where Kodi never been installed so far. So there is no problem with the OS or Kodi itself. My HTPC have LibreElec OS, ad this another PC have Windows 10 x64. It even does not display me those 3D walls backgrounds neither....
I have looked into the Kodi log, but dont know if there is something important. I have uploaded it here:
https://pastebin.com/MgiQSuK2

I ran into one thing, which I dont know what it means. When you go into context menu, where the option "update library" is, there is also option called "scan to library" ....what it does? When I click on it, it simply write "There are no video files in this path"..what it tries to do?
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