did you add any command that plays BGM ?
if you have the RTP BGMs, while playtesting your game, try to press F8 and in the console copy-paste this :
AudioManager.playBgm({ name: "Battle1", volume: 90, pitch: 100 });
do you hear the Battle music with this command ? (battle1.ogg, you could change "Battle1" by any filename you have in your bgm folder, just don't include the extension).
if you can hear something, then you probably messed up with playing BGMs in your game. if you can't hear anything with this line of code executed, it probably means a plugin f*cked up something, or your project is corrupted somehow.
EDIT : also check if you haven't turned off BGM volume, if you have any plugin that allows to change these options (master volume, bgm volume, bgs volume, ...)