So I think you have a misunderstanding of how the reflective environment is calculated with SSR. When you disable the ‘Capture Every Frame’ it does not disable SSR, but rather takes a screenshot of the reflection environment at that moment. Increasing the quality to 100.0 does have an effect, but not to the degree in which you explained.
You also need to understand that it is not the metallic value that is the sole contributor to reflections, as it mostly relies on the ‘Roughness’ value. This is why when your materials roughness is at 1.0 you do not see any reflections. I highly suggest taking a look at our documentation on working with the reflective environment and understanding how to set it up properly so you get clean results.
Reflections
What you are seeing and reporting is the direct effect of Temporal AA and how it is calculated. This in turn adds a slight grainy jitter to the reflections of your scene and can cause them to be a bit unpleasing and unclean. As you can see in my example I provided, the SSR is still being accounted for in the Scene Capture even though it is a static image at that point.
Screen Space Reflections
You can see in the SSR documentation how Temporal AA affects the flat surface showing the reflections. Try setting your Anti-aliasing to FXAA instead to see if that helps. All in all, this is not a bug, but rather a limitation of Temporal AA and Screen Space Reflections working together.
Thank you,