I get a warning “Removed 1 rows containing missing values (geom_point).” when plotting using density_plot_type scatter.

This happens because when using scatter, some points are jittered and may end up visually outside of the plotting range, so they can’t be displayed. That warning informs you (in a cryptic way) of this fact. Given that the jittering is randomised, sometimes you might get that warning, sometimes you won’t, even for the same input.

If you want to silence the warning, use suppressWarning() when you print the plot for displaying.