Ah looks like you might be right. I still have the ??? under Expedition/Critical and looking through my list I don't have the Complete Mission Challenges he has in the pic. Down the Grabbit hole we go once again. I'm tired of all the bugs/lack of content in this game and think I'll just move on. Maybe in a year or so they will have the game that should have been released in the first place but for now I'm done. Thanks for solving the issue and maybe one day they will fix it.
EDIT: Link to the post on reddit https://www.reddit.com/r/AnthemTheGame/comments/bgj1w1/psa_legendary_freelancer_challenge/
Lmao...grabbit hole! I can certainly understand your frustration, I think all of us are frustrated with the issues. But I am still having alot of fun playing even thru the bugs and issues. I am hopeful that it will get better with time. Now I guess it's time to start a new pilot and replay the story line to unlock my legendary freelancer!
Despite my previous comment a buddy and i made a new pilot (actually we already had one due to the collectable glitch for runes) and ran back through the story. It was still showing as ??? right up until the end once we finished Dax: Emerald Abyss and the Return to the Heart of Rage (We didn't need to do Mathias Triple Threat again) It checked off the "Complete Mission Challenges" and finally completed the Legendary Freelancer Challenge netting a total of 10,000 coin for the 2 challenges. Hope this helps others finish the challenge.