I’m having a problem getting the optimal picture on my PAL SNES with OSSC (using the PAL SNES RGB cable with luma on sync from Retro Gaming Cable). I have used the PAL profiles by Opaque79 as a starting point, but I can’t seem to get it right. I can get a sharp and stable image, but there are some weird horizontal “shadows”. I have a screenshot below that illustrates my problem:

You can easily see it in the white text (which should be all white inside) as well as the pixels to the right of the black borders of the title text. It looks almost like some sort of shading.
I’m using Line5x with the 256×240 optim. mode. I have tried messing around with the advanced timing options, but I can’t get rid of the shadows.
Does anyone recognize what the solution might be?
I have an old HD-TV with SCART connection, and I did not notice the shadows when connecting directly to the TV. However, my main goal is to capture game-play footage. The shadows appears both when connecting to a monitor with the HDMI output from the OSSC as well as connecting to as computer with a capture card.