The last 4 terminals I found were unable to play the video. I just got a blue screen saying Sorry, this video cannot be played at this time. I have the achievements though. When I go into Halo Channel, the videos for terminals I have found are still locked.
start the missions one more time on normal and find the terminals once again while being connected to xbox live and not be disconnected.
I saw the videos but I didn’t unlock the achievements. Not a single day passes without encountering bugs or other probelms with this game.
Having the same problem as Exarathas. Found some terminals that I missed during my Legendary playthrough of H2A, watched the videos but the achievements didn’t unlock. Restarted the xbox, replayed the missions on normal, hit the terminals but still no achievements.
I can watch all the videos on the Halo Channel, but not terminal 14 because it thinks I haven’t unlocked all the terminals. What can I do except watching Terminal 14 and 15 on youtube? Because if it can’t be helped I’ll never unlock terminal 15 either.
Hoy no se ha podido desbloquear logros 
Las terminales se desbloquean aunque no las logres ver, solo tienes que volver a acceder a ellas.
Los logros no te los marca pero si vas a Logros en el Xbox One, si te los va contando.
So I know have found every terminal in the game, and have the achievements to prove so, but there are still 4 Halo 2 terminals that are locked in my Halo channel. They just say “Play Halo”. I have even gone back and found them in the game again, and still nothing, just a BSOD telling me it can’t play.