Thanks for the feedback, I have released a post game update based on bug reports from other players, judging by error logs there doesn't seem to be an issue with the number of sprites on screen - I initially designed the game for consistent rapid fire when the B button is pressed but it sounded terrible - The issue more seems to be I placed a bit of code where these sprites initalise rather than where collisions occur and this caused a race condition when the game gets faster than the enemies spawn.
Great feedback on the sounds, I don't have a physical console and the sound files for collisions are actually different, sounds like they're not different enough for the consoles speakers to make out, I'm looking forward to getting my hands on one so I can try this stuff in person!