Here's the chart I tested just now.
I had been using an all-in of 3000 rpm which was the default. Given jhv48's comment, I tried lowering that to 2000 rpm. Still with vacuum advance set to zero to remove that variable. Still seeing the same behavior. The app provides realtime feedback, so I was able to cruise at about 2500 rpm and see the advance clamped to 36, but still get the hesitation and surge on quick accel.
On the way back I noticed the amp meter needle bobbing toward 60 with acceleration. I don't remember it being so sensitive to rpm changes previously, so I'm wondering if that has any bearing.