That's odd. I've never had that happen before. I was told on the Discord forum the "play music" command is a legacy command and it is better to use play sound even for music (since you can loop them), but I never had the music command not play. Is the music file still in the game folder? I sometimes deleted important things by accident when getting rid of extra assets. If you have Discord, I find the GDevelop server has been a really good place to get answers to these types of questions.