Here is a side-by-side of my clean footage in the preview, export settings, and what the renderer is doing to the footage. It compresses it and adds odd noise/grain, and I don't know how to fix this. It looks fine in the preview, but it renders all grainy.
6,000x4,000 ... wow, I'm not used to seeing such massive framesizes for exports. Out of curiousity, what are you doing with them?
What's the original camera frame-size?
And just doing a quick bit of mental math, target of 219Mpbs ... might be way low for that frame-size. As really, 100 to 130 is pretty minimal for UHD, and this is a TON more pixels per frame than UHD.