I believe that's one of those quests where the sites have a chance to spawn the item when you approach them, if you've hit all the sites on the planet and can't find the forth I'd suggest leaving the planet and coming back and doing it again and again until eventually you find the item in a remnant site. Sometimes it takes a while and sometimes your lucky, I personally also dislike this system very much and would prefer fixed sites for this stuff just so I can get it done.
I found the devices and once inside the vault you discover, I found a crate but it looked bugged and couldn't opent it. Once ryder interacted with it he said 'hmm lez see what's inside' but then nothing happens
I think it's another bugged mission. I have about half a dozen now that cannot be completed. We paid to beta test this game.
There is a similar quest on Eos in the south east part of the map where all those kett buildings are.
