March 2017
I just spoke with Captain Sommers in CSEC HQ and convinced him to not kill that guy, but during the conversation, he was invisible. I tried to take a screenshot, but it didn't work for some reason. He was visible when I walked up to him sitting on that couch, but once the conversation started, he disappered.
March 2017
Screenshots not working is an old bug and I don't know that there's ever been a fix for it. Him disappearing could be due to camera angles in cut scenes. Not sure why it happens, but it does. It shouldn't effect your game though.
March 2017
Try to repair the game. (in Origin > Game Library > right click ME3 > Repair)