Looking at the pictures, it's hard to tell, but you might be just not putting on the clearcoat slow enough. Most people are scared of it and try to put it on like regular paint.
You have to watch the leading edge and watch it shine. Practice on something black and you will see what I am talking about. Slow down and put it on thicker.
I've painted COUNTLESS mirrors and it's a pain. It's hard to see, but these are sanded down with just a scotch pad and some mold release spray to clean the plastic. Then 2 light coats of high build primer than sanded with 400 grit smooth. (Hard to see, as the primer I used was black)
Of course I used automotive grade paint out of a gun, but still the process for you is the same..
Paint ONLY - no clear
and when all said and done. (no sanding/buffing required)
I would maybe sand yours with 600 grit lightly and not go through the clear.. just knock it down smooth and re-apply that clear slowly as I was saying.
When I paint, the base lays down fast and quick... clear, I have to slow it down and let it build up for the high gloss. Key is to know when enough is enough, or you get runs!