I resolved the issue (so far). On PS5, after persistent crashing on couch co-op, we were ready to give up.
We tried turning off the internet each time, but it got to the point every time we got back into the game, it just immediately crashed after any movement.
I turned off auto-save, and I have not had a single crash since.
I really hope this works for everyone and that Larian looks into what’s causing this.
