OK, So I wrote my post here
but nobody seems to be able to help. I thought I’ll try to ask for help in Customer Support.
Essentially, I am stuck in this storyline where you rescue heroes. The last quest to rescue Jaina Produmore was completed but then Borvar does not have anything next for me. Am I missing some achievements? Thanks.
Hello Celdorlock!
This is likely that you are referring to!
In short, these quests are currently split into chapters and each chapter is unlocked the week/reset after the previous one was completed. If you only just rescued Jaina during this week, then you will be offered the next chapter in the following reset.
Hope that helps!
Thanks. It helped. Although, I am surprised it is not unlocked. This is my alt and I have already done Twisted Corridors Layer 8 on my main character 
EDIT.
After considering it, I am deeply disappointed.
It makes sense to postpone unlocking Twisted Corridors to week X since the expansion release. That gave those players who had been left behind time to catch up. It makes much less sense to lock progress between chapters to other players who started playing the expansion much later. It makes absolutely no sense to keep locking progress for players who already has got certain achievements. This is again another completely unjustified game constraint. Looks like I need to wait for another week while today and yesterday would be the perfect time to complete all chapters. I have no words for that!