Didn’t Receive the Darth Nihilus Portrait

For both instances it was the Heroic raid. We were doing a quick run to use little tokens so one of our members wouldn’t miss an O66 raid. 

Hey man! They retired certain of the portraits when new content was released. Similar to how you might be able to get a portait for a certain character during its release, but can’t get it later if you missed that opportunity. Here’s a similar post from before where someone had a similar issue to yours. There’s a little bit of explanation there as well. I believe the information is still current. Hope this helps: 

I did not receive the portrait of Darth Nihilus | EA Forums - 12073967 

The Darth Nihilous portrait is "Earned by getting Rank 1 in the Sith Triumvirate Heroic raid."  Tell me something, then... which difficulty were you playing on?  If you ranked first on the Normal difficulty, you cannot get it... you only get it with the Heroic difficulty.  If you are certain about you and your friend ranking first (on separate occasions), then I recommend seeing which difficulty you did it on.  I do not think it is a bug, but regardless I wish you well.  God bless.

- GodIsOnTheMove