There is something wrong with the clicking, as if the hand cursor was blocking my clicks. Did you set its mouseChildren to false?
Also sometimes the bubbles are too far to the edge or barely visible. I'd round their spawn range and alpha values.
Also it's worth stopping their movement, lowering speed to default, or at least stop increasing it after finishing the game. I hope you're removing objects once they're not visible anymore.
Nevertheless, simple yet enjoyable game