I have completed other ones with less damage but I am now at the 75 million version.  I make sure the Boss is still alive, I do it after the reset yet it still shows 0/75M at the mission screen even though my damage is shown in the encounter.  Yes, I am doing this in the Nightmare difficulty as listed in the "Clan Mission".  Restarted several times and have even cleared cache.  

Not sure what I can do to get this resolved, can anyone help please?

Thank you,