Losing local files

[sytzeapers]

Plan

Premium

Country

Belgium

Device

(Macbook Pro, iPhone SE)

Operating System

(latest)

My Question or Issue
Spotify keeps losing track of my imported local files. Local files (aspecially relatively recently added files I feel) are showing grey in my playlists. It usually helps to change the filename on my HD, then it shows again in my local files in the Spotify app and I can play it again in the playlist. But soon after it doesn't anymore. It's rediculous doing this every time I want to play that certain song or album, plus when I want to shuffle my playlist these local files will never be played. Is there a solution for this?
Thanks for your help