A lot of people are having problems with the AMD CPUs and Nvidia GPUs. Some people have had better luck dissabling Nvenc.
Quick Sync and Nvenc do not have unlimited acceleration. I think the 12 core and 16 core AMD CPUs can computer faster than the Nvenc dedicated hardware if the AMD CPUs are as good as AMD users claim. That might be why we are seeing so many issues with AMD CPUs and Nvidia GPUs systems. Nvenc and Quick Sync will make a quad core CPU scream but might slow down a 16 core CPU. That is just a guess. I have also felt a motherboard BIOS update might help.