Hi Christophe, thank you! The visualization should use the settings from B-spline basis section, i.e.
$bsDegree=3;
$CPtsNum=4;
$bsKnot={ConstantArray[0,$bsDegree],Range[$CPtsNum-$bsDegree+1]//Rescale,ConstantArray[1,$bsDegree]}//Flatten;
They were reset in Solve the fitting problem section, then I forgot to set them back for the visualization.
Sorry for the inconvenience and thank you for catching the bug! I'll update the notebook tomorrow.
