Walking around with your party you should hear banter every 20 minutes at least. I had the bug but fast traveling and resting at camps fixed it for me. No banter for nearly 20 hours and now it happenes every 10 to 15 minutes.
It's an insidious bug since you can go so long without even knowing what you're missing out on. Had no idea Blackwall had such a sense of humor :/
It's more complicated than that. Triggers don't proc at a set rate. As best I can tell, it has a % chance to shoot each time you do X, where X is a large number of things. 10~15 is an estimate based on regular play, but plot related banter from characters or your Inquisitor can "replace" banter.
Basically, does your party banter? Are you using three characters that you haven't really used before? Are they talking, at all? Beyond that it's hard to say. I've "thought" I might have the bug a few times, only for it to get wildly crushed as what I'm doing slightly changes and the flood begins.
Cole talks a TON in Crestwood, but I heard no quest-independent banter while doing the huge sidequest there. Other times I had a long string of it at about 5 minute intervals after taking a high level group of "new" characters I hadn't used in a while to clean up lower level quests in zone I hadn't been to in a while.