The same thing just happened to me today. My multiplayer loadouts and armor all got reset to the defaults but I thought nothing of it. I've been doing each campaign mission on solo legendary each week for the challenges and I finished the Infinity level today and found I lost all the others I've done before that. It shows I've done Dawn, Requiem, Forerunner and Infinity in the commendations in the spartan hub but now they're locked in the campaign... wtf?! Right after the matchmaking update like you said.
