Rouz, I can't say much about the peculiarities of the artifact, but from your image above (which overall nicely shows the absence of artifact!), you can tell the trajectory of the artifact is not following that of a ring feature. The true F-ring would appear to have the greatest separation near the extremes of the ring ansae, and then almost disappear as you move away from the ansae, due to perspective. Your feature has its origin near the ansae on the right side, and then proceeds to increase its separation from the main rings before disappearing. That's not what any real feature would do.
This sort of false ring also appears on the limb of the Moon after processing, but it also tends to occur somewhat randomly on some regions of the limb but not others. I'm sure it comes down to the way in which the raw data reacts to the processing, with some regions more prone to generate an artifact than others. Similar to how some regions of the globe, or the main rings themselves, will react differently to the same level of sharpening. For example, your image above shows a strong contrast separation between the C ring and B ring, but this is strongest towards the front of the rings, near where they meet the globe, and fading elsewhere . Each part of the image behaves a bit differently.
Very nice images, and the polar hexagon is looking really good!