Question Losing Saved Progress- Legendary Campaign

So I’ve been doing the campaign on legendary so I can get waypoint armor but the game says I still have 2 missions to do on legendary, even though I know I did them. NBD, I’ll do them again–but when I go to start the mission it says I’ll lose any progress. Does that mean I’ll have to do ALL the missions again since I’ll lose the saved progress? I really don’t want to do everything over.

Any answers?

Thanks.