Sounds like you guys got cans of GW primer from a bad batch. I used there primer for c.20 years and only very occasionally had problems. There are some known issue with them that this happens from time to time. I've had the same problem with Army Painter.
There are a few questions - first, did you shake the can for the full 2 minutes? If the paint's not atomised correctly, it'll come out badly.
Second, what's the humidity like where you are? High humidity can ruin a primer job.
Third, did you apply multiple thin coats or one thick heavy one? The heavier the coat, the more slick it is in my experience.
Fourth - what types of paint are you applying over the top?
There is a trick where you can loosen the paint by standing the can in hot (but definitely not boiling) water to help it flow, but you then still need to give it the full 2-minute shake.
There's a somewhat lengthy thread over on a GW-focused forum (Dakka) where a guy did a proper test (using a micrometer to measure the thickness of the coat) on a whole bunch of different spray-on primers and found the GW and PP ones were the finest (in terms of actual thickness on the mini).
If you have a yard/garden/garage to work in, getting yourself a cheap airbrush and compressor off amazon or ebay and a couple of bottles of Vallejo air primers is hugely more cost effective in the long term. Put it this way, my buy in to airbrushing was a (approximately) $120 compressor and airbrush set and a bottle of black primer ($20 I guess?). I must have sprayed over 300 minis with that one bottle of primer and it's really easy to get the hang of.
If you want something you can brush on, I've heard good things about gesso - but not tried it, I hear it takes some practice.