It's been a while but IIRC if you progress too far without finding them, they will no longer be available if you backtrack. I can't remember the exact specifics, but like for example if you killed the first boss without finding all of the remnants that appear before him, they may no longer exist after killing the boss.
I am more sure that after killing the final boss of the wing, any missed remnants will be gone and you can't go back and try to find them.
Like I said... been a while, could be wrong about this, but might be a possible reason why you couldn't find some of them.
Edited by valenwood_vegan on January 9, 2024 10:48PM
I haven’t killed the final boss in the blue area yet. Looked carefully the first time I did the run in this section, always looking at Alcast’s map, but saw only 2 remnants. They are pretty visible, and not that many places to hide them, so kind of strange that I missed 3 of them.
I have now very carefully run through the whole blue area three times, after having finished the first boss, but cannot discover more than two remnants. Ran up to the secret boss, but nothing there. Ran to the last boss, but found nothing. On vVH there are supposed to be 5 remnants in the blue area, right?