Mine seems to have reached a meta-stable state after running for a few hours around 320/704, where the ball with less area is bouncing almost vertically, and a nearly flat border between the two.
This is very interesting, mine did too, but with an even narrower dark patch.
It is like an attacker-defender equilibrium situation where the vertical guy runs up and down a trench and the attacker tries different paths for orthogonal attacks.
https://i.ibb.co/7bNTtsK/daynight.png