I too wet tumble and have a thing about clean primer pockets. How long between cleaning bras and loading brass? Note that the primer ignition hole can stay filled with water for quite some time after the outside and inside are dry (as in days). I'm betting the hole had water in it and either damped the primer material, the charge directly at the ignition hole, or both. Apply heat or dessicant always when wet tumbling, or give your brass several days to dry, spread out, agitated regularly, and put in a dry environment (indoors).
K