I took some autobody classes, and basic paint classes from a local community college in the 1970's. This was when Dupont Centari was used a lot, and Imron had just came out.
One of the "new" primer-surfacers we used was Dupont 100S, I think. I tried mixing and thinning a batch of it for a project, and thought I could get away with some non Dupont thinner, and it just made a lumpy jelly.
I still think the main problem was the SPI activator in the Global basecoat.