The quest, “Demonic Remains” is bugged and making it impossible to progress.
The quest says:
- Complete Challenge Rift 8
- Kill Chaos Herald Pyl in Challenge Rift 8
I completed Challenge Rift 8, and so that part of the quest is checked off, but Chaos Herald Pyl is not spawning as the end boss. I have completed it two other times since, hoping he would spawn after a few tries, but he has not. I saw a forum post stating that it is bugged and won’t work above Rift 6, so I defeated Rift 6 again and he still did not spawn as the end boss.