In the area Exploration - The Fissure - Narrow Tunnels, is an explorable that involves fighting a few tough oozes. (See the screenshot below for the specific random)
In efu IV, and until very recently, this used to drop an Ioun stone. (An item that was automatically on the ground) And while I understand this item being removed, for it was powerful indeed, this random now has no reward at all.
(https://i.imgur.com/zltvWti.png)