I'm not sure what I did, but my banter is working fine now...for the first time since I started the game in november. Or at least it's working fine in the last 2 hours and I really hope it stays that way.
I started the game today at 06:50 (CET) and I had banter at (party Cassandra/Varric/Solas):
07:04
07:15
07:30
07:54 - But I paused the game for 10 minutes between the last one and this one
08:06
08:28
08:42 - Banter between Varric & Solas started while I was still fighting and both of them were dead at the moment 
All of these were real banter, no environmental comments.
Things I've done differently than usual
- started directly in the Hinterlands (I parked them there the last time I played)
- didn't use the camp tent
- also didn't fast travel once until now (I was too scared to break it again)
- once the game loaded I didn't load another save
Things I've done as usual
- cleared codex and journal
- used quick save a lot
I've also noticed that I have my armour sound back. I haven't hear that since my second or third playthrough and now I'm on my seventh.
I'm not sure if it is because I created a new character or if I'm just lucky today. I really, really hope the bug is gone for good. But I'm not getting my hopes up just yet, even if I'm super happy right now.
Edit: And my armour sound is gone again. I had to restart the game. I'm curious if my banter is gone too now.