We’re using canvas to draw on HTML5, and there are subtle rules in how it handles anti-aliasing. Namely, edges between two shapes sometimes show the seams. The solution here might be to use BitmapData instead of Graphics, as scaling will not scale up the pixel scale being used. You might be able to do it using getPixels then manipulating them directly, or using fillRect, I’m not sure how the performance would compare, but worth trying?
There’s also a define called -Dopenfl-disable-graphics-upscaling that might help as well