I don't know any of the particulars but one of the recently departed negotiators was Andy N. He wasn't there very long. He served on the EGL Negotiating Committee for years and numerous small gains outside of Section 6 were made during his tenure. To be clear- that can only happen with willing participants on both sides, but he had a mutually respectful relationship with management, and both sides benefited.
Andy so impressed the NMB that he took a Leave of Absence to join them. When he left, the EGL MEC Vice Chair commented that he was generally the smartest guy in the room during negotiating sessions.
As I said, I don't know the particulars but losing that caliber of an individual so soon after getting them is indicative of the systemic dysfunction of this (dis)union.