Legendary campaign glitch on halo 4

My brother was playing solo on legendary and got to the end of midnight, he then had to shut the xbox down to go to work when he came back it had reset him to reclaimer and on the mission select screen it said that he had never played the other missions, this has happened to him 3 times.
can anybody shed some light on what is happening or what he can do to stop this from happening and finally finish halo 4
thank you