Colossus Boss and Corrupted Nexus Map Node

Defeated the Colossal Boss and the corrupted boss did not spawn. The area is cleansed but did not complete corrupted nexus quest.

Same just happened to me. Killed boss in Tier VII Forge map Corrupted Nexus after dying once and getting warning that other enemies and content would be removed on revive. The corruption boss didn't spawn after killing on second attempt, but surrounding area on Atlas is cleansed.