When do I stop sanding primer?

I am painting the steel tank, plastic side covers and plastic tail. Right now I’m applying the primer (House of Kolor, KD 3001 black DTS primer)
I shot three coats of primer, but the tank had a small spot where the outline of bondo I used still showed through. In trying to blend it I sanded through the primer. (320 grit). So I reshot another three coats.

In trying to sand it, if I use a maroon scotch-brite pad it leaves a finish that looks and feels smooth. You can see some cross hatching, but it feels as smooth as glass. But if I hit that with 500 grit sandpaper it looks like orange peel showing through.

Should I shoot the black base coat over the scotch-brite surface or do I do I need to use the 500 grit sandpaper?

These aren't great pics, but the first shows the finish from the scotch brite. It shows some cross hatching, but is smooth as glass.
The second pic show what looks like orange peel if I hit that with 500 grit.

Wet sand with the 500 grit until smooth and flat and peel is gone........ Scotch Brite scuffs but will not get it flat.