Hmm. I blew my arena matches this morning, already. So I am simply lucky until proven otherwise. But I have a hypothesis.
Maybe the "bug fix" screwed up? I was testing a killing blow first chance I got. Of course it didn't work. But maybe it does something else, and it makes Humbling Blow land everytime, thereafter, instead? Like until you restart your client?
It might be I just got lucky, but this was happening the day before, too. And yes, I tested the killing blow patch that day, too. I used a couple refreshes yesterday, trying some new strategies, so I had plenty of matches. And I put QGJ in every comp, including with my droids!
I must have had close to 20 matches since the patch, and my QGJ has been on god mode. 100% except on the two times, early, when I tested a killing blow. And that trial on Foresight, lol. Of course, winning was still important to me, though, and I only started going out of my way to pick the hardest targets the last 3-4 matches or so. I probably landed Humbling Blow >1.5x per match.