I feel that it's the primer, too. Most likey, a thin spot in the primer, caused by sanding.

If it were mine, I'd strip, and start over. Failing that, I suggest that you sand, as Ken suggests, and dust you first few coats, giving the paint time to flash off, between coats. Make you final color coat a normal. "wet", coat.


Next time, take a look at automotive primers. If you prefer aerosol, Duplicolor would be my choice.