Hi Steve -
Bummer to read of your primer issue, I can think of nothing that makes it work so well for me, and not for you. Here is what I do, first ensure the contents are up to room temp, then a good mix with metal paddle to stir up the solids from the bottom. Next a thorough blending with electric mixer, then transfer into mixing cup, add thinner, blend again and have at it.
I have used X20A, Tamiya Lacquer thinner, MC Leveling Thinner and iso alc, all with about the same results. I thin heavily, usually 50/50 to start, then maybe end up at 70% or more thinner. I rely on multiple coats for good coverage, laying on enough for it to actually work as a primer, for filling and sanding.
If you have not already binned it all, maybe give it one last go????? For reference, I use Badger and Iwata gravity brushes, and shoot at 15-20psi. All work as intended, one bit of info from me, I use only the gray primer, the white is problematic for me, and the black is less than great for my use. Seems sort of chalky or slightly gritty.
However it ends up, I hope you can source a supply that works well for you, agrivation is an unwelcome visitor on any guys or girls hobby bench.
Patrick