I switch to Sherwin Williams Promar 400 flat, sprayed the ceilings 3 times and when they dried they have spots, didn’t dry to a smooth finish. I didn’t have this problem with PPG Porter flat paints.
Promar 400 is a cheap contractor flat. It won't stand up to a better paint. Should have used the Promar 200, much better paint at a good price.
If you want to use the Promar 400 try adding some Flotrol. This will help it dry smoother. Don't know about the spots. If they are small spots it could be something bleeding through the paint. Use some Kilz to seal up the spots and respray. Need more info about the spots.