what do you consider a lot of shaking, IF I have use for a rattle can, I shake it for three of four minutes, then I warm it in a bath of very warm water. THen I shake it more,, and more, then heat, then shake again. I would be leary that the nozzle is clogged or messed up, like someone started to use or spray it, then did not invert and clean it.

also keep in mind that primer is primer primarily because of the particulate matter in the product. Keeping that in mind, if that can sat for months or years, it would not be a surprise at all that it would need a LOT of shaking. I mean 10 to 15 minutes coupled with hot water bath. It can settle out very hard.

I much prefer the DC 540 and it does need a good sanding before a color or top coat but I have not ever gone back over the primer with a seal coat....
  But then I tend to first seal coat and fill all balsa wood before the DC 540 primer....Lately with non taut Butyrate dope but before with Nitrate dope

DC 540 primer usually sprays good, drys fast, and sands easy once dry....pity my Napa is 56 miles away and only ever has 2 cans on the shelf

The DC-540 is the good stuff. I had terrible results with the white Duplicolor primer too, but my problem was it hardened too much for a good sanding job. I really like the Perfect Match Duplicolor acrylic lacquer paints, and they spray right on top of the primer. I like their adjustable nozzle and triangular spray pattern too.
Rusty