Essence Boss not droping atlas skill point book

As the title says, I saw that I needed a t11 stone to get access to this area. I grinded to T11's and gave it a shot. Killed all the imprisoned monsters causing the boss to be buffed as hell. Killed him after dying 3 times. The greater essences dropped, but the atlast 2 point skill book didnt drop.

Does this boss not currently drop the book, and was I misreading that, or is there a bug where its just not dropping from him?

I have the same, please FIX IT!

Just had the same experience 5 minutes ago, killed the boss after dying a couple times, it dropped a few T15 maps, some greater essences but no skill book.

The map doesn't count as completed, even though I killed everything inside.

I had the same exact issue with the map where the bosses spawns in succession inside a stone circle, seems to me like special map won't reward you with a skill book if you die once.