I tried it and it started playing the music right away for me.
Preload sounds doesn't work with music, it states so in the description. Music is streamed, meaning that is being downloaded as it plays.
You could always try to move the sounds from the music folder into the sounds folder inside C2 and that should preload it correctly but it would increase the game loading time.
https://www.scirra.com/manual/141/files