Act 4 Prisoner fight stuck campaign

I killed the prisoner in Act 4, but died just as he did. Now I am stuck and can't progress the campaign.

I tried killing him again, and I can hear the black guy landing, and he is there as there is an invisble area blocked, but I can't see him or interact with him.

Also tried with the help of someone else using that person's instance, same issue, can't see the black guy, but I can hear him.

So I don't know how to get my character unstuck. Just starting over is faster but this needs to be fixed. Either create a way to restart a quest, or just fix your system.