I copied my music library from my mac to my PC to be able to play my local files in both computers but there's an issue with some files - they work in one computer but are greyed out in another computer. If I then switch out those greyed ones in one computer then they turn grey in another computer. This shouldn't happen.
Not sure if I found the cause but it seems that in Spotify Mac client those greyed out songs are 1 second longer or shorter. From the example pictures the greyed out song shows 1:03 in Spotify for mac while in Apple Music (Mac) and in metadata, iTunes (Windows) and Spotify (Windows) and Windows' metadata it shows 1:04.
So It's more likely an issue with Spotify Mac client.