Hey there,
usually there shouldnt be a problem with volumetric clouds.
I m working on some issues with the high resolution Render at the moment. And got the Feeling, that it has something to do, with Lumen/Raytracing.
Our results differ between “normal Renderings” and high resolution renderings.
We had nbo issues with our clouds, but with our shadows.
What I would recomend for faster iterations to render it in “normal” HD, you get the same errors as with a larger resolution but a lot faster
All the best, and let me know if you fixed it