EDIT: Not a bug, see last post.
So, according to Taran’s World, we’re still in “cycle 15” for the Soul Forge. There are still 7 Mythics that haven’t made an appearance as part of this cycle. However, Champion of Anu has shown up again before these other Mythics, and is already part of “cycle 16”.
Bug? Weird quirk?
(edited to correct myself)