I’ve read a few threads from 2015 that where having the same problem I’m now having I cannot progress as the game will not load mission unconfirmed, on previous threads it stated load mission as new game tried that didn’t work, has there still not been a fix for this???. Update have tried restarting both the game and the previous mission meridian station still cannot progress to level unconfirmed Microsoft/343 if this is a clitch get off ya back sides and sort it out 3 years no resolution what are you playing at!
Try reinstalling the game. Sounds to me like maybe a corrupt file of some sort. However, it’s a big game so that may take some time.