Last level: Music only plays once without loop / last boss possibly bugged?

[Firebeam]

First I would like to appreciate the work done here, it's a piece of my childhood that was missing.

Anyways, I did play all of it but I did notice the issue on the title. At the last level, music plays only once and then music falls silent (no other gameplay hindrances detected) Also, I never finished the game before so I don't really know if I need to do something else, because it does seem that any weapons fail to register damage on the boss. I know that this game has very minimal damage feedback to the player, but either I missed something or any projectiles fail to register collision at him.

Keep up the good work!