achievements not working.

So ive heard a few people who bave had problems with unlocking achievements, but am I the only one who has completed halo 4 solo legendary, but it didnt track properly? It says I have completeted all on solo legendary in the mission selection. But the achievement trackrr says im missing 2 missions. Xbox support were extremely unhelpful. Who else has this problem?

You need to beat Forerunner and Infinity again and it’ll unlock for you.