I don't have the field of giants aspect achievement

I have all legendary aspects available in by codex.

I also have completed all 3 dungeons in the field of giants area.

Still, I don’t have the achievement asking to get all 3 legendary aspects from the field of giants area.

Any way to fix this?

the achievement tracking is bugged, it only counts the aspect if you get it for the first time from completing the dungeon, and doesn’t work if you unlock the aspect via salvage.
the workaround before they fix this is to create a char on a realm where you don’t have the missing aspects in the codex, and go do the respective dungeon(s) there.