If you are sure that the title music file is in the assets/media directory and that the spelling is exactly the same in all places, then I'm not sure what the problem would be.
I don't use music in my game.
But, can you check to see if the format of your title music is different from that of the music used in your game?
Does the title music play properly when you run the app in Windows?
And, please, are you working in Tier 1 or Tier 2? This can make a difference.
Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master