On slow strokes, you can the tracking between key points looses accuracy as if the signal between points becomes weak.

I have tried everything I can to correct the issue like changing the stylus battery, 100 point calibration and driver updates. I'm pretty much convinced that N-trig just cannot be compared with Wacom (even the iPad Pro does a better job)

However, there are programs (ClipPaint and Mischief are my prime examples) have built-in mouse smoothing which greatly reduces the jitter but means the drawing action lags behind by a second or so.