When I start the Trial of the elements the normal event quest progression disappears and the chest disappears after the event has completed. I have not been able to complete it after reset.
Yeah ever since new 4 portal primal storm event I have not been able to loot the elemental chest. Always bugged or phased or as you said just fails and despawns. I used to do it EVERY week. Now it’s never doable for weeks on end.
Tried again twice after the most recent weekly reset with the same results.
Was able to find a workaround for this. I flew out of the area and back to the cave which seemed to prompt the quest progression window and i was able to loot the chest.
Wasted my time attempting this again a few days ago, when we killed the last named enemy the chest just despawned zzzz.