First Herald partial progress block

Act 4, Arastas, Excevation boss Benedictus, First Herald of Utopia

If you die after defeating the boss and let the not quite cinematic play out, when you respawn it starts the boss death animation but does not play any of the others and just stops there, the door remains closed and you cannot progress.

Luckily there is a workaround to just start a fresh instance and defeat the boss again.