Halo 3 LASO Loading a Previous Level

This is my first post ever here, so I hope I’m doing everything right.

So, I’m playing the Halo 3 LASO playlist for the achievement. I was on the level “The Ark”, where you’re fighting the Scarab to get into the Citadel. I died and did the standard save-and-quit exploit and booted up the game again… only to find myself in the Scarab battle on “The Storm”. The game is convinced I’m still on The Ark - the pause menu tells me that’s the current level and gives me the same objectives it normally would, and that’s what the playlist says I’m on still. The only thing I can figure is that Scarab battles have similar programming, so maybe the game got confused? I’m grasping at straws.

I’ve tried resetting the game and the console itself, and I don’t want to progress any further because I fear if I get a checkpoint, my progress will be irrevocably lost. I haven’t found any info on this happening before. I’m a new poster, so if there’s anything else I can do, please let me know. Thanks!