Question, are people counting quest banter as banter?
In Crestwood at the moment doing the main quest there... plenty of banter re: the quest at hand, I'm thinking until I've finished the quest then normal casual banter gets put on hold there, can anyone verify?
My banter has been regular-ish, every 20 min or so through my 50 hours so far (approximately... haven't been keeping that close of an eye on it) 
I think this is part of the "problem" not related to the bug (which I believe does exist) and people testing should be aware of it. Judging from my observations I think every time a character quips something it counts as banter and resets the timer. At least that's what my experiments yesterday showed: I had a lot of banter until I went to the Storm Coast, where I had environmental comments in about the same frequency, but almost no banter.
I think this is a problem because a oneliner ("I like the sea") is wholly different for the playing experience compared to a conversation that spans a couple of lines at least.
Still, if you are testing, please keep this in mind (and do note the region you're in).
This would also mean that you would get MORE banter in regions you have already explored, because the environmental comments are exhausted. Can anyone confirm/refute this? At least my testing shows it might be the case, as I get less banter when I am first starting out in a region. Not zero though - I quested through Emprise du Lion today and had about 3-4 instances of banter, plus environmental comments, all in all something about every 10 minutes, I'd guess. The banter got less frequent the more I explored, but this might just be because the frequency of the combat increased at the same time...
Why I think this is unrelated to the bug: in my PS4 game, I have almost zero banter. When I went to Emprise du Lion in that game, I had zero banter, only Cole would comment on everything, all the time (comment/oneliner like "It sings" and stuff like that, no banter). It got so bad that I stopped bringing Cole along because I'd rather have silence instead of constant nonsense talk. In my PC save, Cole plays nice with the party and has really interesting conversations with everyone.