It was probably around Season 6 that I had finally gotten around to playing through the games Playlists and base game challenges. One of the biggest problems I had encountered while playing wasn’t really the enemy, but the Save and Quit functionality. Saving and Quitting at any point in most Campaigns (Most notoriously in Halo: CE, Halo 3: ODST, Halo 3 and Halo 4) regardless of the Iron Skulls effects being active will immediately revert your save back to the beginning of the mission despite RESUMING the mission, whether that be a LASO Playlist or not.
Apparently this is a bug encountered due to the system believing that you are switching versions of the game, regardless of if you’re just simply Saving and Quitting to return seconds later or not. It’s been a thorn in the side of many who play Playlists, but it can also effect those in normal missions. I’d exercise caution, the next time you put down the game and wish to return to it later, due to tedium.