I have done a few experiments on the stuttering problem.
It appears the rendered video turns out fine using 32bitXP and 32bitVP9. I only get the stutter when using either 32bitVP9 or 64bitVP9 on 64bitWin7. No it is not a playback problem as another user already suggested.
Anyone else get problems in 64bit vs 32bit?
I wonder if its a video-audio sync problem…