Update on journal / codex clearing:
I've been playing my new character today and mainly doing the templar / mage / haven quest chain, but I did go to the storm coast for an hour or so and I had 5 banters all in 10-15 minute intervals, sometimes less. Also had few comments on the environment. Prior to that I went to the Oasis where I did have a 40 minute banter silence, during which Cole repeated the same environment comment 3 times.
Edit: Oh and I used different companions for each zone.
Music is still constant, but no sign of combat music. The regular, relaxing soundtrack keeps on playing through the combat encounters. I have noticed some combat dialogue, but it's always strangely muted and doesn't follow any pattern - very random. Sometimes they say something, sometimes they don't.
Still waiting for the ball to drop and for the banter to just stop as it always has. But this seems to work to some extent, I know it didn't for others so maybe it's not even the cause for these results.