Probably planned/conspired to resign sequentially for maximum effect. These are the type of men Mueller hired for his get-Trump team.
"These four prosecutors filed a brief making a sentencing recommendation without getting approval from the chain of command. That is extraordinarily unusual in the DOJ. In fact, I can say it's unheard of at the DOJ; certainly, I've never heard of it. In practice, DOJ lawyers almost always get approval for everything they do."
https://townhall.com/columnists/marinamedvin/2020/02/12/exclusive-what-happened-in-the-roger-stone-case-prosecutorial-misconduct-says-defense-lawyer-n2561231