Achievements not unlocking

Games Halo: The Master Chief Collection
1

I’ve been playing couch Co-op through halo 3 on legendary with a friend and have had no problems unlocking achievements. However lady night we finished it on Legendary and he was got the achievements for beating the last level, and for beating the game on all difficulties. I only unlocked beating the game on Heroic.

That was the only achievement, not even beating the level Halo.

In the progress on the game it lists that i have 9/9 level completed for legendary yet nothing pops it.

Any solutions?

2

update:

I just beat the level on solo, finished it on legendary and managed to get the kill 1000 flood…still no achievement for beating the level

3

I would like an update as well, as I have achievements from the 1st week that are still stuck in unlocking status.