It is generally due to remaining mould release agents left on the hull during production. Sanding might or might not work. Sanding will carry the leftovers fromone point to the other. Clean the remaining flked paint and use solvents to cleanthe remaning mold release, then you can sand, prime and paint. This is very common on new boats. Normally the remaining mold release should be cleaned with solvents before applying the first paint which nearly none of the producers handlers are doing.