Recently, I have a problem with all of my local-file songs in my Spotify app, I cannot listen to them even I already download them. I linked the songs like I normally do (put songs in desktop folder > add them to playlist).
We're sorry to hear you're having troubles importing your local files. Could you give the steps here a go and perform a clean reinstall of the app on both devices? They are more thorough than a regular reinstall and make sure that no corrupted files remain that might be the reason for such behavior. You should also remove all playlists with imported files and start the whole process from scratch using the instructions in this guide. It's a good idea this time do it over another internet connection, e.g. a mobile hotspot, if that's an option.
Hope this helps. Keep us posted on your progress.
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“Music is a language that doesn’t speak in particular words. It speaks in emotions, and if it’s in the bones, it’s in the bones.” - Keith Richards