I have a theory about that. While some of the writings of the Early Fathers, that are today characterized as origenist, are heretical, others are simply teaching about Purgatory in an inchoate form.
Note that origenism is very much about the Purgatory: it states that divine mercy is so great that even Satan one day will be pardoned. The Purgatory, after all, is not a consequence of there being a Hell, but rather of there being a Heaven.
When the Great Eastern Schism occurred, it became important in the East to extirpate any mention of Purgatory in the patristics. So anything St. Gregory of Nyssa, or Origen, had to say about the operation of divine mercy after death was brushed aside as origenist.
I wanted to make a collection of these so-called origenist quotes and publish it on FR in that light, but never found energy to do it.
I’m not sure what you mean. Are you saying that St. Gregory of Nyssa and Origen did not actually mean to say that all souls in Hell would one day end up in Heaven, but just sound like they do because they are talking about purgatory, not Hell?