I have completed the halo reach campaign on legendary with 3 of my friends about 30 minutes prior to writing this. Our completion time was marked at 2:24:58 and they have received their nameplate and achievement. However I was the only one who received neither even though I unlocked prior achievements earlier in the campaign. I really hope there is a way you guys can find a fix for this because I want that nameplate.
(I have picture proof of my completion)
Thank you and please get back to me on this as soon as possible.