I’ve been doing the Chain’s of Domination campaign and a lot of the dialogue from the NPCs are not showing up. The characters I am questing with will respond as if the other NPCs have said something.
This also happened with the “Stay a while and listen” dialogue between Tyrande and Astarii. Tyrande would respond but Astarii hadn’t said anything.
I tried disabling all my addons as well as relogging but ran into the same problem.
I have the same problem
This. I’ve been having the vanishing Dialogue (especially voice acted lines, but text vanishes too) bug since Legion on my account. It’s not just one character, but its more obvious on characters I play more.
This needs to be addressed, especially if Blizzard wants to actually provide decent storytelling in game. And many times the quest dialogue is used to explain the steps in a quest, and when that bugs it makes completing the quest difficult and confusing for players. Most players assume a period of silent npcs means they’re done, so they run off without staying for the story, whether they mean to skip it or not.
I’ve submitted many tickets and bug reports, and it’s never been properly addressed. I usually get canned responses from Support, or they blame it on addons or say just turn in the quests and move on. I’ve tried everything on the standard list of ways to ‘fix’ issues. Reset the quest/RP, removed all addons, re-created cache, even re-installed the game. Nothing works to fix it permanently.
Resetting the quest has very rarely caused some of the dialogue to re-appear, but I’ve spent hours resetting a quest to try to get all the dialogue to trigger. This is not fun or good gameplay for the time wasted trying to enjoy the game. I’ve often had to go to Youtube just to see the entire quest dialogue, and sometimes I’ve seen it bug out on the Youtube videos too!
This bug is most obvious in voice-acted dialogue when there are long extended periods of silence as the NPC moves around as if they are talking, but say nothing. But I’ve seen it happen with text-only dialogue too during BfA. In Legion, even the popup talking head toast windows failed to trigger along with the voice acted lines.
The most memorable instances off the top of my head happened during major story moments:
With more and more lines in game being voice acted, and with Blizzard focusing more on telling story through these RP dialogues inside the game, this needs to be fixed. This bug has existed since at least Legion without being addressed. It causes story to be missed, and results in a confusing story with missed story beats that doesn’t make sense to the players who are missing chunks of the story but don’t even realize its missing.
Please fix this Blizzard.
It is also happening with the dialogue between Jaina and Uther in Korthia. I talk to Uther to begin the “Stay a while and listen” but he never speaks, only Jaina.
no responses from the blues is quite sad even if its a post from them like “we know about this and working on it but no ETA on when it will be fixed” it may not be a bug but a technical issue … there are a few posts about this over in the technical support forums… if reinstall windows or world of warcraft or playing around with the ingame settings and still have this problem then it must be on the blizzards server side of things and needs to be fixed
It’s also happening with Alleria and Veressa in Oribos. 
Edit: They seem to be working since the pre-patch. 