From what I can gather after reading everyone's posts and my own testing it seems that sound related issues and timing seem to be the common denominator. Almost everyone is experiencing some issues with background sounds/music/ambient noise in some form or another and having trouble triggering party banter.
I'm assuming party banter is triggered in a few ways; by reaching certain areas, performing certain actions and 'random' party banter that seems to be time-based (ergo; you're suppose to get a party banter to trigger when roaming about every X minutes). If working by this assumption it's likely that there seems to be something off with the way the game tracks time and the passing thereof.
This is supported by the claims that quests don't always show 'completed' immediately after completing them, certain audio not triggering or triggering later (combat music, area music, effects, ambient sounds etc,etc.). It seems the game is 'late' to respond, thus missing certain triggers unless we manually 'reset' it. We do so via the 'Haven-Hinterlandsx2-Mount/Unmount-rest' tricks. This temporarily works.
Unfortunately this reset only works for a bit, till the game goes back to tracking the 'wrong' time, being late again. This is supported by the fact that our workaround doesn't last and needs to be repeated with each start up/load/new area. Every time the game loads up something new, it 'forgets' the timetable we reset it to and goes back to being late.
At least, that's my theory, from what I gathered here. Problem could be in the way the game tracks time and triggers internally.