Originally Posted by Plengrock
It's bc you got a secret achievement and then you reload checkpoint but you did't do it again. I think you have to do all secret objectives in one playthrough, not get all secret achievement in one playthrough. If you reload you still got achievement but not completing the secret task.
Your probably correct on this, you need to pick up the item you can't just load back a checkpoint and then still get miss know it all as you need the collectable in your inventory.