I FOUND THE SOLUTION GUYS.
I can confirm 100% this has worked for me.
https://www.reddit.com/r/BattlefieldV/comments/9xihbd/how_to_fix_glitched_war_stories_challengesletters/
Product: Battlefield V
Platform: PC
Please specify your platform model. PC
AMD or Nvidia Model Number : GeForce GTX970M
Enter RAM memory size in GB : 16GB
Which part of the game is the issue happening in? Single Player War Story
Which part of the mode? Tirailleur , Égalité
Please select your region Other
On which server did this happen? Single Player
When did this happen? (dd.mm.yy hh:mm) 13/11/18 08:25 AM GMT
Summarize your bug: Optional Challenge not completing.
How often does the bug occur?: Does not fix itself
Steps: How can we find the bug ourselves? No idea, maybe try completing the challenges and resetting your war story status over and over again
What happens when the bug occurs? Challenges marked incomplete in main menu, does not communicate reward unlock to server
What should be happening instead? Giving me the rewards and fully completing the War Story.
Just writing to say this isn't limited to the Under No Flag War Story, I can confirm this happens on the second Tirailleur campaign as well.
Did your game also looked like it was about to Crash when either finishing the mission ?
Because mine did, it didn't crash but i think that's part of the reason.
No, my game was stable. I restarted the mission once when I was detected, then did both challenges at once and let it play until I got to the third mission.
