The attached test script produces a blank plot, with
faint grey gridlines. However, the left-most vertical
gridline is drawn over the x1 axis, and both x1 and y1
axes lose their tick markings beneath the gridlines. I
think the gridlines should be drawn at the back, behind
all of the axes.
Therefore, I think you need to draw all of the
gridlines from all of the axes first, and then draw all
of the axes and tick marks over the top?