Thank you so much for finding it. I couldn't replicate it myself. It detects if you move out of the area2D and teleports you to the other side. Based on this I'm assuming its because you can fully escape the area2d once you get teleported due to moving at the perfect angle to not capture your collider anymore. Perhaps the solution would be use a distance check and teleport rather than a area2D.
In hindsight making the character white and the stars white wasn't a smart idea. I actually spent half my time trying to create a good inventory/upgrade system and ended up scrapping it.