Skyshards in the imperial city were reset and can be picked up again. I noticed it a couple days ago when I was in IC on my main, I came across a skyshard that I could pick up. I thought that was weird, I could have sworn I picked up the 6 IC skyshards on my main years ago. So I checked on an alt that I know for sure picked up the 6 IC skyshards about a year ago, went to IC and found on that toon too the skyshards were all up again. Double checked in the achievement too, it says those skyshards were previously collected but all skyshards are back up.