My Xbox One achievements disapear?

I was playing Black Ops 3 and I was doing some zombies achievements until I realized, the achievement completely vanished from my list. I was playing Ascencion and there are a total of 3 or 4? So I started the match and played. I got 1, which is to fly the landers. But the others are gone? Can they become secret... show more I was playing Black Ops 3 and I was doing some zombies achievements until I realized, the achievement completely vanished from my list. I was playing Ascencion and there are a total of 3 or 4? So I started the match and played. I got 1, which is to fly the landers. But the others are gone? Can they become secret achievements? They’re completely gone. Idk what to do to bring them back.

This happened to me before during a campaign mission in COD WW2. I got the reward after some time and actually another I got without notice. But this hasn’t happened yet to my BO3.
0