Several autocephalous Eastern Orthodox Churches have already backed out from the upcoming planned Pan-Orthodox Council all citing different reasons. The Bulgarian Orthodox Church pulled out early, claiming a number of issues needed to be resolved before there could be a council. The Greek Orthodox Patriarchate of Antioch backed down because it wants nothing to do with the Greek Orthodox Patriarchate of Jerusalem. Both the Serbian Orthodox Church and the Georgian Orthodox Church pulled out over the council’s plans on ecumenism with non-Orthodox Christians like us Catholics. Several Eastern Orthodox clergy gathered for their own synod to declare Catholics along with Protestants as heretics, thus the Catholic Church should not be called a Church. The Russian Orthodox Church on the other hand has thoughts of not attending.
An Eastern Orthodox priest, Fr. Philipp Iliashenko, even described this upcoming pan-Orthodox council as like “a Congress of the Communist Party“, noting the necessity for all autocephalous Eastern Orthodox Churches to attend and for unanimous agreement on any given topic.
To be realistic Ecumenical Councils have never required unanimous agreement; otherwise you could never get anything solved. No wonder the Eastern Orthodox Churches have not had an Ecumenical Council since the Second Council of Nicaea even though that itself did not have unanimous consent. Several heresiarchs such as Arius presided at the First Council of Nicaea. Several Protestants, even John Calvin, were invited to the Council of Trent. Such a move of course is to help bring them to the light of faith, not because their heresies matter.