I bought a new salvage item and try salvage many green and yellow items, i can't get runes or sigils from its.
Because you don't get them. The salvage item will automatically salvage all sigils and runes.
Was I able to help you or give you a hint? Click on Helpful and/or Thumbs up, I would appreciate it alot!
When you encounter a bug ingame, at first you should file a ticket via the ingame command /bug, as only this way the devs will know exactly where you were, when the bug happened.
It's chance to salvage (break down), not extract (remove/recover).