Sounds like to me, its an activator bad or going bad.
If it sprays dirt (sand look) its activator.
If say half the hood was sprayed and looked good then as you are spraying the other side dirt starts appearing on the side you first started with, that is ISO clumping, not dirt or static. One clue is they will be black, gray and white specks of dirt.
Extreme solvent trappage can do same thing but has to be really bad.