We can see an error message in InkViewer. What does "Decoding Error: NoCoordBeforeCoord" mean? The strokes were recorded correctly.
This is normal behaviour – it happens if the pen fails to decode any coordinate just when starting a stroke, which may happen e.g. if the paper quality is bad at that spot, or the light conditions have changed between the previous stroke and this one.
The functionality is there to be able to detect if a single pen has some camera problem, or the paper quality is not good.