I know how Petras works. Last completed run shows deaths but they were all prior to entering the wish. No one on our fireteam died atfer entering the 13th wish.
Maybe that could be ... The wish only activates that if someone dies all of the fireteam will be thrown out of the raid and if you make it to the end you will get the triumph But before and after the wish is activated, nobody is allowed to die That could be the answer