As a big Uncharted fan, I set out on a quest to platinum all the games. I've done so with the remasters, 1 and 2 on PS3 and Golden Abyss on Vita. But U3's thrillseeker trophy for completing a competitive multiplayer will not pop for me, no matter how many games I do. I contacted ASKPLAYSTATION on twitter, who then directed me to PS live chat supported. They tried to help the problem, I was instructed to first restore the file system in safe mode, which unfortunately did not give me the trophy upon playing another game. Next he had me delete Uncharted 3 from my PS3, and rebuild database, then play another game which also didn't work. Then I was directed here by him, saying to talk to the developers to see if they could add the trophy to my account.
TL;DR the trophy wouldn't pop no matter what so I was sent to see if it could be added to my account or not.
P.S. I saved the chat file if necessary