I just curious..u bought the game or u got it free? Itch.io dont notify to me u bought the game here, anyways i want to help u!! :)
I bought it from IndieGameStand when it went on sale this weekend, but it seemed like they only have a Leave A Review section, not comments & I felt comments section was more appropriate for my needs.
Okay, I'll try doing the fight as intended. As I'm testing a speedrun route, I had just run around the bosses into the loading trigger, which seems to work fine for the first 2 bosses, it'd be a weird glitch for just the third boss to be effected; it's almost as if the screen becomes extreme right justified when the loading trigger loads the next scene, although if it is just meant to load the end cutscene, I don't understand why I'm able to fire but it might be in context when I eventually see what is occurring on the screen.