Yes! Lowering the FPS fixed it. Thanks for the fast response, @wittaj
By the way, I had it at default and the default for Substream 1 (lurchy) is: 30fps, i frame 60, 256 bitrate.
And I didn't have to go down as far as 15 fps. The video was "lurch-free" at 20 fps, i frame 20 (whatever that...