I think this is the key passage;
Once the Rumbek diocesan see became vacant in July 2011, a Comboni Missionary, Fr. Fernando Colombo, served as Diocesan Administrator until December 27, 2013, when Fernando Cardinal Filoni – Prefect of the Congregation for the Evangelization of Peoples at the time – appointed Fr. Mathiang as Diocesan Coordinator. Thus the announcement of Carlassare’s appointment on March 8, 2021 would mark the end of nearly a decade without a bishop in Rumbek. Mathiang served as Diocesan Coordinator for over seven years before Carlassare was announced as the new bishop. The assassination attempt, reportedly incited by Mathiang, came seven weeks after the announcement.
I'm thinking Fr. Mathiang enjoyed his job as administrator and didn't appreciate the arrival of a new bishop. As another poster said in jest up thread...."nothing personal, just business".
Okay, thanks. That’s helpful. Could be financial shenanigans that would be uncovered by a new Bishop.