The reason for the cessation of Eucharistic communion between Moscow and Constantinople is understandable to everyone - this is the actions of the Patriarch of Constantinople regarding the church schism in Ukraine. As you know, the Patriarchate of Constantinople recognized the Ukrainian Orthodox Church as autocephalous.
Moreover, the Patriarchate of Constantinople announced the restoration of rights to the Kiev Metropolitanate, although more than 300 years ago these rights were transferred to Moscow by Constantinople. It - political a decision that cannot be explained by any religious considerations.
In addition, the Russian Orthodox Church is very unhappy with the ambitions of the Patriarch of Constantinople on the status of "first among equals." Unlike Catholicism, in Orthodoxy there is no “one and infallible pope” who would have power over all Orthodox churches. Therefore, the claims of the Patriarch of Constantinople on leadership are considered unfounded. Now, parishioners of the Russian Orthodox Church will no longer be able to receive communion in churches under the jurisdiction of the Patriarchate of Constantinople.
By the way, in 1996 the Eucharistic communion of the Russian Orthodox Church with Constantinople was already suspended. Then the Patriarchate of Constantinople established its jurisdiction in Estonia - from political, of course, considerations. Events are developing in the same way now, with the only difference being that tens of millions of Orthodox people live in Ukraine, now caught between a rock and a hard place of church schism.