I tried some of the possible workarounds and clearing my journal was a bit strange.
In the tab for completed quests, roughly 80% of all entries were marked with the "new" icon, some were marked as read. I don't remember ever visting that tab, but i might just not remember looking at it at some point.
Then i went through the list and cleared all the "new" icons.
When i returned to the game, i got 2 minutes full of "Quest Complete!" notifications.
That suggests the possibility of those quests being in some kind of faulty state. I haven't seen anyone else mention this, so it might just be an isolated issue.
The rest of my post is just me theorizing about this and easily dismissed if the bug i mentioned isn't widespread 
In my case, banter triggering and trying to use one of those quests as the topic might just result in ingame silence if that causes some kind of error. That could also explain why one area works well for some people, while it causes complete silence for others. What if the whole party wants to talk about that awesome quest and everytime they try they bug out? Meanwhile, someone else didn't do that quest or it simply completed correctly and is in a valid state.
A main quest in a faulty state might just kill most of the banter for all areas.
It could also make the whole thing harder to reproduce. If i was tasked to find the cause for missing banter, the general course of action would to look if the banter trigger is firing and what could prevent it from doing so. If i didn't read about missing audio even if it is triggered, i'd probably equate "triggered" with "hearable ingame and working as intented".
Then again, this would point to a problem with the savestate and would be easy to reproduce with the saves they analyzed.