There is something in your layout that is making the song stop or restart, otherwise the music would continue playing on its own. My guess would be that you are doing something like this:
At start of layout -> Play music
If that is the case, what you need to do is add a tag to the music that you are playing, then add another condition to your event like this:
At start of layout
Audio tag "music" isn't playing -> Play music
OR alternatively, you could just remove the At start of layout -> Play music from all but the first layout.