Why are some tracks not playing on Apple Music?

I've been using iTunes for many years, and had personally loaded up several thousand music CDs to it, and when it was replaced by Apple Music I found I can't play all these tracks, only some of them. Even more confusingly the tracks I can play and the tracks I can't often come from the same CD. My playlists are preserved, but also suffer from the same thing - I can see most tracks but they won't play unless I can also see the artwork I have uploaded, if the artwork isn't visible the track won't play. Also Apple Music seems to have replaced much of my carefully chosen artwork with artwork I haven't chosen, and it won't let me upload the correct artwork. Moreover I can now see and play many many tracks that I have never bought or uploaded and I can't see how to delete them.

I was very satisfied with the old system - the new system is a very poor replacement.

Has anybody got any experience of this sort of thing?

[Re-Titled by Moderator]