DNxHRHQ to Quicktime export problem

I'm trying to export a Quicktime from a UHD DNxHRHQ sequence to send to Resolve for grading. I've tried ProRes4444 as well as DNxHRHQ exports. As soon as the files are taken into Resolve and then some colour grading applied, they all exhibit colour banding, heavy image degradation, pixelation and macroblocking errors.

Any ideas how I can make an export that doesn't have these problems?

Ta.