And just now, it worked for me aswell. The solution still seems to be winning over & over again on the starfighter assault maps, until it acknowledges this on the challenges tab post-match. For me, it was "The Aggressor" which was still bugged & considered unfinished, now I've won on the map with the Death Star debris, and through finishing "The Aggressor" (which was already claimed for like a month now), it finally unlocked "A Tremendous Service" for me.
Same man, I was playing Starfighter assault for 6hours and I got the milestone randomly.
