Apokatastasis was quite properly rejected as a theological error, indeed, as a heresy, at the Fifth Ecumenical Council (although I do believe that Emperor Justinian acted arbitrarily in anathematizing Origen for his belief in apokatastasis, when St. Gregory Nyssa also believed in it, and Origen was as widely respected for his piety in the third century, if not more so, than St. Gregory Nyssa in the fourth (whose importance unlike that of Origen, who was individually and uniquely vital in the Church of Alexandria, was that of one of several pro-Nicene Christians known as the Cappadocians, including his older brother St. Basil the Great, and his older brother’s best friend, St. Gregory Nazianzus, neither of whom expressed a belief in apokatastasis).
The last denomination where a belief in apokatasis was common was the Church of the East, where we see it reflected in the writings of the Assyrian monk St. Isaac the Syrian and lastly in The Book of the Bee by the Assyrian Metropolitan bishop, His Eminence Mar Solomon Bassorah, dating from 1222 AD. Since that time, the Church of the East has rejected Apokatastasis.
It should also be stressed that Apokatasis as believed in in antiquity, and Universalism as believed today, by, for example, members of the Unitarian Universalist Association, are not the same thing. Indeed, the idea of Apokatastasis as viewed in antiquity is, I think, best summarized by this quote from The Book of the Bee:
That said, I do reject this as an error, in line with the overwhelming consensus of the early Church; I believe that CS Lewis instead properly expressed the truth of the matter when he said “the gates of Hell are locked on the inside.” That is to say, scripture indicates there are people who are so filled with hate that loving God would be impossible for them, and so, tragically, they are binded by their boundless capacity for self-destructive hated.