many times during color correction I render all the noise reduction first. then I export that piece as a prores file, then place it over the rendered clip. I do this so I can grade and render in the future without the hassle of the long render times. the issue is, if I don't manually turn off the fx in the lower track first, it still renders like it is rendering the clip below it also. I feel like a clip with 100% opacity should ignore FX on the clips below it. I believe fcp legacy operated like this. not sure it's been a while!