I tried firmware 0.72 and it does not seem to have an effect.
I have not hooked up my GB-8220 because it is a pain to get hooked up and configured correctly again, but I did try s-video into a iscan pro and I could see the same horizontal wobble that I see using RGB on the OSSC.
If anything the wobble or wave looked more “digital” when using s-video to the iscan pro to the OSSC. Like I could see that the offset was exactly one pixel and it looked more like a square wave.
So there seems to be something on the sync signal, but I don’t know where to go from here…