Recently I have been noticing color banding / artifact issues on black screens whenever the Ultra needs to upscale sub 4k content to 4k. This behavior disappears if I change the roku to output 1080p instead of 4k and let the TV upscale. I've noticed this behavior across all apps whenever the video source is being upscaled to 4k. I've attached two screen shots for reference. Both pictures are from the end credit sequence in the Vietnam documentary on netflix. I've observed this behavior in uncompressed blu ray playback as well so I don't think it is an issue with the stream bit rate changing. It's possible to workaround this issue by leaving the roku in 1080p and manually changing it to 4k whenever I know I am watching a 4k stream but I would prefer not to have to be changing the output resolution all the time.
My current setup is ultra -> receiver -> 4k TV
1080p Output Resolution (1080p source content)
4k 60Hz Output Resolution (1080p source content)
Thanks for any help you guys can offer.