Why are my apple music tracks greyed out in a playlist but can be played in the library?

I've just switched from Spotify to Music and used SongShift to transfer my many playlists, but I've encountered a problem. Strangely, the tracks in my playlists, and I mean most tracks in most playlists, are greyed out and can't be played. Despite this I can search for that track in the search field and play it direct but, as soon as I re add it to the library - grey and unplayable again. I've checked to make sure my library is synced an the computer is authorised. I've even had a go at different playlist transfer apps but it's the same issue each time. I should say this is the case on my iPhone (13 pro IOS 16.2), Laptop (M2 Macbook pro Ventura 13.1) & iPad (16.2).

Anyone got any thoughts as to what it could be? Apple Music is pretty useless to me at present.