At first, I was using my C64 Reloaded but found that using a regular C64 with a lumafix produced a much nicer picture (although it could still use some fine tuning). I think the SMPS on the Reloaded board generates some interference with the output video signal.
For some reason, both with the Reloaded and the regular C64, I see that the picture is pretty stable for the first 30-60s and then suddenly it starts to judder as if the phase shifts a bit. If I reset the RetroTINK by using one of the buttons on it (or power cycle the C64), it is again stable for another short while. This is not related to the OSSC since I get the same noise when I hook my TV directly to the RetroTINK output.
So which menu did you use to change the adv. timing of the C64 signal? If I use the 240p menu, nothing that I change in there seem to make any difference.