Im seeing the same problem as with the slot machine in chapter 2. So this box has the ability to hide items to pass detection. But youre required to have a S ranked magic engineer skill... I can make excuses for the story myself but i think if the reader have to bother themselves for that, the writer is failing his job unless its a mystery or something. It feels like way too specific and too convenient.
Author really just need to say "you wouldnt be able to get this box this early but because i got the copy and amplification skill, i could get it and use it in this event." which would give some background and depth that would complete its sense.