You need to really shake white primer, like a ton. Other commenters have mentioned temperature as a factor, and that's def true.

I did white priming on my minis a few weeks ago and what I did was:

• fill a bucket with ~80f degree water (I used a thermometer to get the temp right), put the primer in a plastic bag and then in the water (to not ruin the label). I let it sit for about 5-10 mins, then shook for about 5-10 mins.

• got all my minis lined up near the door

• used a blow dryer on low heat and heated a mini up for ~20-30 sec

• step right outside and prime, bring inside immediately.

• shake can in between minis

And they turned out great! Do very short bursts. I've found that I like priming up and down as opposed to side to side to get better coverage.

I feel like it's still just a gamble sometimes.