I have just discovered a weird thing about the music disappearance. It said next to some songs, the song could not be found in the location and wasn´t uploaded to icloud because of an error. After I then go and delete the song but don´t tick the box delete from icloud the cloud download symbol appears next to it and it becomes playable again. Weird! But has anyone else noticed that who has had problems with disappearing music from mac iTunes library? I also use iTunes match. Maybe this helps others recover their songs too.