It was in the Red Grave, there is the quest with the Huntress to kill the grave guardian. In the level the mini boss patrols the circle and there are graves open. So I interacted with a grave and it turned into an adversary, and at that very moment the grave robber ran towards me, but after the fight the mini boss disappeared even though there was no fight with him and since then he has not appeared anymore and the quest is still open. even when I sleep in the tavern he does not come back even though he still has to be there. It must be a bug.