Halo 3 MCC PC Achievement bug?

So i just completed Halo 3 on legendary and for some reason in the missions tab it says i completed every level on legendary but got no achievement and when looking into my service record the missions Covenant, Cortana and Halo says the highest level of completion is Normal. I really hope i don’t need to redo those missions over again.

you probably need to do it again, I had this happen to me for the storm and the only way I could get it to count was by playing through the previous level and going straight to the level I needed from there instead of the menu which was really annoying. At the very least I was able to start the previous level at the farthest rally point

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> you probably need to do it again, I had this happen to me for the storm and the only way I could get it to count was by playing through the previous level and going straight to the level I needed from there instead of the menu which was really annoying. At the very least I was able to start the previous level at the farthest rally point

Yeah that did it finally got the achievement. Thanks for the help