The Ancient Shrouded Armor and the Sneak 100 perk works/takes effect as you click the stick to go into Sneak mode. You should see whispy black clods that roil around your character for a moment, then they fade. It's the effect of the Perk taking effect where it would make an enemy in combat momentarily lose you and have to search for another target.
But the Perk's ability takes effect as you go into Sneak mode.