Finished chapter 3 campaign, no achievement?

So… I finished chapter 3 of the campaign (on heroic), which was way too long and somewhat annoying in my opinion, but anyways after the end of the mission nothing popped up.

What gives guys? Does this mean I won’t get an achievement for completing the campaign cause the game thinks I never got chapter 3 even though I’m currently in chapter 4?

This is some nonsense, really.

it happened to me also. I played co-op but when i played the mission over
again solo on legendary and it gave it too me.

Its weird that it does that. Also when i completed that mission it gave me the achievement for completing the game on normal lol