Unable to claim reward although I've completed the milestone

I play in the U.S.A. on Xbox One btw & I’ve been grinding in starfighter assault because supposedly THE AGGRESSOR and/or THE DEFENDER are bugged (showing as completed but aren’t) thus preventing me from getting the big reward for A TREMENDOUS SERVICE. Now after the starfighter grind, I’ve completed SLOW DOWN, YOU WILL & SIESMIC CHARGE & UNDER 12 PARSECS. I now have 4 Completed milestones for which I cannot be rewarded. This is totally unacceptable.