Sometimes on the circles game mode, the balls will merge and end up yeeting one off into the stratosphere, which loses the game. This happened to me when the playing field was only about 50% full.
I think that maybe balls which have enough upward momentum to approach the "game over zone" (for lack of understanding on what that's called) should bounce off of it with a reset in momentum to keep the bounces from setting off a chain reaction.
Here's an example of a stratospheric yeeting for reference: https://imgur.com/a/8TbzT7e