I just started collecting the skulls on Halo 3. The 1st few I found recorded as achievements in Halo waypoint, but the last 2 I found have not. They appear on the in game skull selection menu, but are not uploading to gamer score on waypoint. Also I just found another, and it is not even showing up in the in-game menu now. I am on an xbox.
i believe there are some skulls you get but give no achievement.
I literally just held the skull in my hand (avatar) on the 1st level, but no sign of it anywhere on the in-game menu, or halo waypoint! I jumped up and down with it. I dropped it and picked it back up. I ran with it for awhile. No skull recorded. WTF!
Maybe try reloading the level, and doing it over. I know right where the skull is, shouldn’t be that difficult to get to again.