Can't join to my friend's lobby, as he can't join mine. Tried a lot of solutions but they are don't work. Any advises?

Did anyone else see that?

Thinking about buying this game but mainly to play the coop campaign together. Does it still work? And how exactly does it work? If he is hosting and Im joining then do I have to progress my character on my own? Or does it just copy progress he has? also what about DLC?...

I've never played Co-op before and wanna play mainly carver because i haven't seen that story I'm willing to do NG+ or a fresh start

I was browsing thru my old games looking for ones that i finished but never completed the achievments and i just noticed that the unobtainable achievement is gone after all this time. Great, now ill be able to 100%.