Spotify shows all my local files

[aromeroshow]

Plan

Premium - Familiar

Country

Spain

Device

Macbook Pro Retina 13'' 2015 - iPad Air 2 - iPhone 8 Plus

Operating System

macOS Mojave 10.14.2 - iOS 12.2 - iOS 12.2

My Question or Issue

I've always used my Mac for adding local files to my playlists and syncronise them with my iPad and iPhone. But ever since last week, I was not able to play some of those files on my iPhone: some of them had just disappeared, and those I could see I couldn't play them.

So, I erased them from my playlist on my Macbook, and wanted to add them again. To my surprise, Spotify Desktop showed all my local files, even though I just selected to show one specific folder. 

I've tried erasing the app and installing it again, but the problem persists.

I just want Spotify not to show any of my local files, apart from one specific folder, so that I can add all the songs in that folder to my playlist and see if it works on my iPhone and iPad.

How can I do that??

Thank you in advance!