Took another look at this and I'm 99% sure it's caused by too low of a resolution being used for the volumetrics effects pass.
Just using ultra quality FX mitigates it quite a bit and I'm pretty sure I've fixed it entirely by boosting the internal resolution used for the effect. However, my quick fix is expensive, framerate wise. I'm also not able to test in a ring as dense as the one in CptXabaras' screen shots.
So, if either of you are getting solid frame rates in icy rings with a lot of fog and want to try adding the following to your GraphicsConfigurationOverride.xml, I'd be interested in your feedback:
XML:
<?xml version="1.0" encoding="UTF-8" ?>
<GraphicsConfig>
<Volumetrics>
<Ultra>
<StepsPerPixel>32</StepsPerPixel>
<DownscalingFactor>0.5</DownscalingFactor>
<BlurSamples>3</BlurSamples>
<TwoPassBlur>true</TwoPassBlur>
<StepMultiplier>4.0</StepMultiplier>
</Ultra>
</Volumetrics>
</GraphicsConfig>
Formatting is important, so if you're not able to completely replace the contents of your file, make sure you get the indents right.
You could also use the attached file and place it in "%LocalAppData%\Frontier Developments\Elite Dangerous\Options\Graphics\". Make sure you remove the .txt extension.
Note, as written, this will only work at ultra quality volumetrics/FX. If it works for you, I can try tuning the parameters more to be less impactful and/or work with other presets.