I created an account just to post this. Same problem here as well.
A lot of topics around this issue, for example: https://www.halowaypoint.com/en-us/forums/6e35355aecdf4fd0acdaee3cc4156fd4/topics/halo-5-guardians-campaign-solo-not-resuming/a1efc98c-ab6c-42ed-9afc-d5fa3ecbd14e/posts
The game is totally unplayable for campaign players. I've played every Halo through, some of them many times. But this. Having spent hundreds of euros on the games, I'd have hoped for some (proactive) info or fix plan at this point - almost a week from the update that trashed the game for at least a bunch of people, if not all.
343 have you acknowledged this? Is there any plan for fixing it?
Yours truly, for now.