Abyss prevents campaign map boss icon cross-out

I started a new character, progressed to Act 3.

In Chimeral Wetlands, I found the Toxic Bloom area had an abyssal rift spawn. The boss (Toxic Bloom) was also there, so I cleared them all.

After killing Toxic Bloom, I checked the map and found that Toxic Bloom's icon was not crossed out.

So I went to the waypoint and created a new instance of Chimeral Wetlands and found Toxic Bloom again, this time there is no abyss spawn, and killing Toxic Bloom this time gets the map icon crossed out.