Just going to copy paste my post from the reddit thread.
Hey guys, I have made my dark iron dwarf before prepatch, leveled him about half way, then stopped playing on him. Once prepatch hit, I leveled him to 50, but I have seemed to encounter a bug, or possibly not since this is pretty much my first alt. If my main has started (not completed) nazjatar but has unlocked world quests, has shroud and the catch up HoA, do my alts need to complete all the same previous steps that my main did, or should I be able to access nazjatar right away without doing the war campaign and everything prior? I ask because once I hit 50, I got the heart of azeroth from magni, then there were no followup quests at all, I couldn’t even re enter the chamber of heart even though I have the heart. The quest “What you may regret” shows up on my main map, but once I go to the spot where the NPC quest giver should be, they aren’t there. I apologize for the long post, but I didn’t want to leave out any details on this. I asked this same question in the discord, and there was one other person who is supposedly having the same problem as me. Thanks in advance.
When I do the isquestcompleted for uniting kul tiras, it returns as true which makes me suspect its a bug even more.
Edit: Blizzard has kind of acknowledged this: https://us.battle.net/support/en/article/000275307