Pretty much the description. So using ffmpeg. If you have a yuvj420p video, in my case 5k HEVC, but I think h264 would also produce this problem, and you scale it using scale_npp filter, then encode it as h264, both sides using the NVENC/DEC you get a green video.
If you use the NVDEC resize filter -resize, without scale_npp, the right video is produced.
I think this is some bug in scale_npp, ffmpeg 4.2.