I'm sorry, I really can't diagnose the issue. I thought it might have to do with whether multithreading was available or not, but I tried exporting a WebGL version with multithreading enabled and it still ran into the same problem. From some online Googling, your Windows CPU doesn't support multithreading but your Mac CPU does. I think this has something to do with the Godot 2D physics engine that is out of my control, I was aware that my game was pretty intensive on the physics engine but didn't have time to optimise it before the deadline. I might have to ask around people that are more familiar with this than I am.