During a Whisper dungeon of Tunnels of Tul Dulra on Penitent, I completed the Mastery objective of killing enemies in the circle to summon Sanguine Champions. Once the timer ran out, the objective changed to kill all remaining enemies as expected.
However, there are no more enemies to kill and the objective remains the same after 5 minutes.
The Event is not completable.
Teleporting away and using the portal back to the dungeon did not remedy the issue.
Knowing Blizzard’s laziness and how they don’t actually summon new enemies, instead shoving them into inaccessible areas of an instance (occcasionally you can spy these enemies in certain circumstances) and moving them to simulate them being summoned, my assumption is that this is what occurred. One of these enemies still exists in some random inaccessible area of the map and was never moved to the Event area.
TL;DR:
The event, Ritual of Blood with 5 statues, bugged at the end seemingly believing there were more enemies to kill.