Blizzard knows this is an issue. See the pinned blue post saying they’re trying to figure out why this is happening.
On top of all the corpse generating issues, if you die fighting the WB in Nahantu, your minions won’t automatically resummon when you revive unlike in other areas. They probably used the original code when making the expansion and forgot to update it to the current version. So without the ability to generate any corpses, your ability to fight the WB in Nahantu is over if you die.