Playlist progress reset... except it didn't?

Has anyone encountered this bug yet?

On the Halo 2 LASO playlist, I am currently struggling in Gravemind. The campaign says 11/15 complete appropriately.

When I wanted to resume progress just now, it booted me back to The Heretic while still saying 11/15 complete. There’s even the blue completion bars below all missions up to Gravemind. I can now only Start instead of Resume and have no option to resume my progress. It’s still shown but I can’t access it.

Do I really have to start from the beginning despite the game showing me the missions are completed?

I swear if I have to go through Cairo Station and Regret again, I’ll cry myself to sleep tonight…