My guess the Dev team is adding new feats on the wiki which is going to appear in the next update. I also just happened to have found Frantic Rage on the forum recently even though I’ve made a couple barbarian research myself about a week ago and didn’t see it when looking at the list of other feats which requires Barbarian Rage as a prerequisite without Frantic Rage being part of it.
Of course there’s also the possibility I might’ve missed it... But it’s as good as I remember.