Seconding this. I visited 2 of the recent crash site suggesions, and one was below ground moving (bugged), and the other was above ground moving. I then went directly to the coordinates suggested and found nothing, nor anything on the scanner. I'm not sure how these are meant to work, but it seems bugged.
Instead, at HIP 14479 just pick a planet (I chose HIP 14479 7, the furthest out with rings) and circle around it (around the rings is a good speed) and keep an eye out in the navigation panel for Unidentified Signal Source.
When it pops up, lock the destination, face it, and see if it's an "Anomaly Detected (Threat 4)" one. If not, move on and keep looking.
If so, exit supercruise just like any other destination when in range. Gently bump the object to destroy it (5-10k an hour. if it's too slow, you'll move it forward, try harder), and you'll get 1-2 fragments to cargo scoop, each giving you several towards the 25. I did 4-5 USSs to get all 25, and it took about 45 minutes. I did miss 3 USSs by not paying attention.
Just keep going around the rings, but they'll pop up seemingly anywhere in the system at random.
Here's a tutorial video for USSs to get Unknown Fragments:
https://www.youtube.com/watch?v=FGqju_aWync