"The Silent Cave" unique map not completing after killing boss

I killed the boss of the Silent Cave unique map, but it didn't register completion of the map.
He dropped all his essences, but not his atlas passives book.

Think maybe its because my minions killed him slightly off my screen?

As you can see in the screenshot is evidence that he's dead. But the map objective still shows incompletion.

Idk if I'll ever be able to find another one of these silent caves in my atlas again since it seems so rare, if I could just get my atlas points that'd be great.