no worries!
cannot repro on my side, with either of two stock units. weird that you don’t see missing pixels with a screen.rect() fill 
i’m assuming you’re on latest OS?
i’m curious what happens if you do a line fill:
function init()
redraw()
end
function redraw()
for i = 1,128 do
screen.move(i,21)
screen.line_width(1)
screen.line(i,55)
screen.stroke()
end
screen.update()
end
edit: @jemfiner also, what happens if you init the draw in your original script at the number value that represents the point where pixels go missing (rather than using encoders to navigate there)? trying to sort out if it’s how it’s getting there or what…