A very, very short guide that should solve the problem with achievements staying locked despite being earned. Hopefully soon to be obsolete.
Solving the Glitch
Posting this as I found a solution to a problem that some people are having but not many are discussing.
Unable to unlock mission completion achievements?
- Turn off competitive score/time completely.
- Turn off all skulls and launch mission 1: Noble Actual.
- Press escape and return to mission select.
- Reselect the mission you want to play.
- Readd skulls.
- Reselect competitive time/score.
- Play and complete mission.
Achievements should unlock.