There was some page towards the end I remember being hopelessly lost and never recovered.

You mean yourself or the plot? I think that in the third act Egan added some weaker elements both as a corollary of the idea being explored and as a way of introducing some traditional action, in a novel that is otherwise mostly the setup of an elaborate thought experiment.

Nonetheless, I think the result is extraordinary, because the problems posed, the paradoxes highlighted, and some brilliant insights, are new and valid outside the fictional world created in the novel.