Adding to this, I'm also having issues with the music shuffle option inside of Big Box.
I have a .m3u file attached to a game and inside of LB it shuffles the music perfectly.
In Big Box though, I have it set to Auto-Play Music in Game Details and Shuffle Soundtrack Music, the music begins playing on the game details screen but it is always the 1st track and hitting play next track will always play the 2nd track.