Nuggets

... I didn't get the achievement. Did this happen to anyone else? It says I have completed 25 Challenges, but my achievement didn't unlock. Should I try to complete another Challenge so it might unlock it?

Unfortunetly, you need to complete the whole chapter/episode online, so it progress it to towards Mark VI armor completion. I completed campaign Legendary Co-Op, but got disconnected during the 5th Chapter, Reclaimer. Did it again on solo, got disconnected right at the end. During the third time solo Legendary, I didn't get disconnected and I completed the whole Chapter online and then I finally got the armor and emblem. If you try to connect back during the Chapter, it still thinks you are offline. Maybe going out and back to the checkpoint might help, if you get disconnected during the Chapter. (Sorry, if it was hard to understand, what I tyoed) Basically: Complete the game without getting disconnected during a Chapter/Episode.