While playing through on legendary, there is a point in the mission "Reclaimer" where you are on the mammoth and an unidentified ship arrives and shoots a green beam towards the ground. In my game, and I know that I am not alone, the ship never comes even after destroying a very large number of wraiths and ghosts. This process took me at least an hour only for me to find out afterwards that the ship that was supposed to come never came and that the game simply quits progressing at that point. The very last event that ever occurred in the game was a new warthog showing up with two spartans in it. They hopped out and proceeded to aimlessly look and jetpack around the area. After that, nothing, just silence and waiting and the obscure checkpoint trigger here and there. I haven't yet tried restarting the mission just because of how long it took me to reach that point.
If anyone knows a fix for this please let me know; I can't find one anywhere.