Phyletism. The Greek Church (Constantinople, Alexandria, Antioch (then), Jerusalem, Cyprus) or the Church of Bulgaria, depending on your POV.
The Patriarchate of Moscow has had many, for the simple reason of the great numbers, the expanses where dissidents could hide in remote areas. In the other Churches, the flock is more managable size, and hence can be brought back into line more easily. The hiearchy has done its job trying to deal with correcting them. Enforcement was only the problem, particularly during Communism.