In the last part of the last DLC mission, when I am supposed to talk to Elsa after preparing the defences of the hotel, she won’t talk to me and the mission comes up as finished. No final battle against the waves of machines or nothing.
I did finish this mission on a friends session, but that shouldn’t mark it as finished on my playthrough, should it?
Hey @Deviant 
This is not intended, the mission progress you got from completing the mission in MP should not have carried over to SP, but did so due to a bug.
We are aware of the issue (mission progress carrying over from MP to SP when it shouldn’t) and are working on a high priority fix for it. The fix will hopefully be in our next patch.
Unfortunately, even if the fix makes it into the next patch, it will not “un-finish” your already completed mission so that you can play it again, the mission will remain completed.
If you want to play it again you’ll have to play it in someone else’s MP session, or create a new save.
Sorry for the inconvenience and thanks for reporting! 