Confront Kanu and First Herald stuck bug --- HELP

I'm playing Poison Pathfinder. When fighting First Herald, he's dead while talking.

Now whenever he says "I'll bury all" and do the whole screen earth quake he will disappear and the door of the excavation site never open nor any earth quake happen. The screen only shakes for some time.

I tried to respawn at the last check point, but he keeps saying the line then disappear. When I went back to Character Selection and returned, he's not there, the quest stayed still. And I need to respawn again for he to reappear, saying same line and disappear

Help