User blog comment:Master Sima Yi/Assassinews 03-12-'14 — New Assassin's Creed in Victorian London leaked/@comment-5174994-20141209170427/@comment-3046679-20141209201905

That's because some artifacts in like, 2 last rifts, are locked unless you've played the companion app. Otherwise, you're screwed out of getting them and 100% sync.