I did some testing, and im not 100% sure, but it seems like the music is just muted when pressing "a" (not sure if spamming or just pressing is the key), right after you pressed Space to exit the playtime disclaimer. Sometimes the music was gone for me, sometimes it wasn't. I think you'll have to try spamming keys after pressing Space to find the problem^^
Not that I could hear the music, I really like it :))