I am not sure where you see that and how but the plugin actually just add the retina images in your src-set, then your browser picks the most adapted images for the current screen and device. This is hard to debug since the browser with your device makes this decision, it will be different for almost everyone.

In my case, it definitely shows the 150×150@2x: https://ibb.co/i1uQ8F
So I don’t think there is any problem ??