I'm confident that they did not know the reason, as if the dynamics were that well understood there would be no "problem" to be solved. I have no idea when/if i

I'm confident that they did not know the reason, as if the dynamics were that well understood there would be no "problem" to be solved. I have no idea when/if it was later explained. Also worth noting that the graph isn't perfectly symmetric but this is presumably just due to accumulation of numerical errors.