I have seen this as well, though I normally keep surrender level set to normal.  However, it is extremely odd to see a solo sovereign with no cities refuse to surrender to an opponent with 8, whose army is standing next to her, ready to kill.

I had Magnar surrender in a game last week.  I think that he was only the second one I have ever had surrender.

I always have Surrender Threshold set to Often, and you still have to have about/at least three times their score before they'll surrender.

Sounds like they have made it harder to get a surrender. I might turn it back on in my next game.

That's been my impression as well, and to be honest, I'm all right with that.

I had Karavox become my vassal last night when he had one city remaining.  But all of the other times in my previous three games the leader of the faction had set torch to their cities and retired from the world.