Your logs shown that MCEBuddy is detecting your nvenc encoder, however ffmpeg is unable to use it:
2019-12-30T21:56:20 MCEBuddy.AppWrapper.FFmpeg → [h264_nvenc @ 00000000028e5d40] No NVENC capable devices found
However handbrake is able to use it with a decent conversion speed of about 98fps.
Sounds like your graphics driver may have changed and is causing ffmpeg some grief. Try changing your driver to a more stable version or rolling it back.
As for GPU utilization see this topic for more details.