Still getting freckled pattern

Hard to say,maybe contaminated or dirty plastic,is it primed,what paint are you using.Newer acrylics like Mig,AK need to be thoroughly mixed,not just shaken there is an another post about Mig paints above.More info needed,maybe pics.

Airbrushes like a certain viscosity range for the paint to be in in order to spray properly. If you're getting a bumpy, speckled or possibly freckled look I bet the paint still is not thin enough. The perfect viscosity is that of 2% milk. I know I know, you don't have to say it but that's the proper viscosity.

The issue called "fish eyes" occurs when the surface isn't clean.

J;

 How well did you clean the surfaces Before you painted? That's what is sounds like. I think " G " hit the nail on the head for this.

Just so you know, fish eyes look like craters rather than raised humps. Some acrylics crater when the first coat goes on too heavy as well, and true fish eyes are as others mentioned, due to surface contamination. There isn't much difference in look between cratering and fish eyes. Those things are different from what I was speaking about in my other message fwiw.

Honestly I'm guessing at what you mean by freckling.