So it starts out great using your intel quicksync hardware encoding cruising along at a decent 70fps with a ETA of about 1 hour for completion.
2018-02-23T00:45:53 MCEBuddy.AppWrapper.Handbrake → Encoding: task 1 of 1, 12.26 % (67.28 fps, avg 69.19 fps, ETA 01h11m30s)
Then your graphics driver throws an error and terminates the conversion:
2018-02-23T00:45:54 MCEBuddy.AppWrapper.Handbrake → Encoding: task 1 of 1, 12.30 % (67.91 fps, avg 69.19 fps, ETA 01h11m29s)Error code -21, hb_qsv_wait_on_sync 602
2018-02-23T00:45:54 MCEBuddy.AppWrapper.Handbrake → ERROR: encqsv: MFXVideoENCODE_EncodeFrameAsync failed (-21)
So then as a fail safe MCEBuddy falls back to software encoding which craws at about 10 fps
2018-02-23T00:48:06 MCEBuddy.AppWrapper.Handbrake → Encoding: task 1 of 1, 0.42 % (11.69 fps, avg 11.56 fps, ETA 08h05m37s)
The issue your graphics driver which is unstable or become unstable at certain times depending on what your computer is doing, maybe the screen saver comes on making it unstable or maybe it goes into power save mode, can’t say.
Try this page to update your driver to a stable version and see if that helps otherwise you may need to turn off any power saving stuff you have going on.