"If anyone does not anathematize Arius, Eunomius, Macedonius, Apollinaris, Nestorius, Eutyches, and Origen, as well as their impious writings, as also all other heretics already condemned and anathematized by the Holy Catholic and Apostolic Church, and by the aforesaid four Holy Synods and [if anyone does not equally anathematize] all those who have held and hold or who in their impiety persist in holding to the end the same opinion as those heretics just mentioned: let him be anathema."
But no mention of apokatsatasis is connected with this condemnation nor in any of the other thirteen anathemas. In the context of the other anathemas, the concern is quite possibly Christological (by this time Origen’s Christology was thought to be problematic, in part due to misunderstandings of his work).
However, outside the main sessions of the Council it appears that some fifteen additional anathemas against Origen were appended. We should also note that ten years earlier, in 543, the emperor Justinian produced nine anathemas against Origen. Both lists, which overlap considerably, concern other supposed teachings of Origen that by then were considered risky or misleading. The idea of apokatastasis is one of these: that at the end of history, all created intellects will be restored to their original condition of union with God.
It is useful to look at the relevant anathemas. From the Council’s fifteen anathemas consider I, XIV and XV:
If anyone asserts the fabulous pre-existence of souls, and shall assert the monstrous restoration (apokatastasis) which follows from it: let him be anathema.
If anyone shall say that all reasonable beings will one day be united in one, when the hypostases as well as the numbers and the bodies shall have disappeared, and that the knowledge of the world to come will carry with it the ruin of the worlds, and the rejection of bodies as also the abolition of [all] names, and that there shall be finally an identity of the gnōsis and of the hypostasis; moreover, that in this pretended apokatastasis, spirits only will continue to exist, as it was in the feigned pre-existence: let him be anathema.
If anyone shall say that the life of the spirits shall be like to the life which was in the beginning while as yet the spirits had not come down or fallen, so that the end and the beginning shall be alike, and that the end shall be the true measure of the beginning: let him be anathema.
Of Justinian’s earlier nine anathemas the directly relevant ones are seven and nine:
If anyone says or thinks that Christ the Lord in a future time will be crucified for demons as he was for men, let him be anathema.
If anyone says or thinks that the punishment of demons and of impious men is only temporary, and will one day have an end, and that a restoration (apokatastasis) will take place of demons and of impious men, let him be anathema.