In the past few days I have completed Halo CE and Halo 2 on Legendary difficulty. Halo CE was completed with a friend in co-op, Halo 2 Solo.
Despite the mission select menu showing completion, I have not received any achievements for Halo CE and my career shows that 0 missions have been completed. Halo 2, however, has given the correct credit and all achievements have unlocked. Previously I completed Halo 4, which also unlocked achievements. Halo CE seems to be the only game I’m experiencing problems with so far.
I’d appreciate help solving this, as it has taken a lot of effort to complete on Legendary and I am working toward Helioskrill armor, which I will be unable to use at this rate…
It’s also worth noting that the scarred armour for completing Cairo Station has also not unlocked within Halo 5.
EDIT - I forgot to mention that when I played through Halo CE, I was totally disconnected from the internet because I had just moved house and hadn’t set up yet. That’s the only difference I can see between when I played Halo CE and Halo 2, which I played while connected to the internet.