Unbearable Whispers IV triggered in incursion

The prophecy requires you to kill a tome dropped by a random rare monster, this unfortunately happened inside an incursion without my notice. A bit after the incursion I noticed the prophecy appeared in my quest log below my minimap.

I cleared the entire map (Tribunal) until /remaining gave 0 left as response. The prophecy did not complete and it was no longer in my prophecies.