round 2 model cars.

Sounds like time to strip it off, give it a bath with soapy water, rinse, dry.  Maybe a light going over with a fine scotch-brite then prime, scuff and see if that fixes the issue.

You didn't say what your prep was so that is not saying what your prep was is wrong, just and idea on fixes.

I've got a round 2 Avanti that I haven't dug into yet, so am interested in if the above, or whatever, works out.

Some, but not all, of Round 2's kits have an awful lot of  mold release contaminating the surface. It seems to be particularly bad on larger pieces, especially with the white plastic. Soap and water seems to be ineffective for me, so I've taken to soaking the parts in Purple Power or Simply Green to degrease the parts before assembly.

Hi;

    Usually I've had no problem . But ,  just to make sure I surface prep any model with the thinner recommended for the paint . Something like taking a tack rag over it .

 I also use a tack cloth but , I have found if you are using one , do not press hard when you use it on plastic or primer .The material in tack cloths can cause what I call frost spots and fisheyes.      T.B.