You may be putting them on too thickly, or just moisture or something with the resin yeah, but honestly many paints will take longer to cure on plastics and resins than they do other materials, also Rustuleum and Krylon primers are kinda ehh in my experience, especially their base ultra covers and such, they're pretty much just really flat regular plaint with the 48 hour+ cure times that entails. The only one I do really like is Rustoleum Universal Bonding Primer, sticks amazingly well to things.
This might sound weird, but the best sanding primer I've found is actually Harbor Freight's Sandable Primer. It goes on a little rough with it's cheap nozzle, but it legit dries amazingly fast, fully dry sandable in 30 mins. Makes a really fantastic quick working filling primer for dent work and such. I was a bit doubtfull when someone here suggested it too, but I'd definitely recommend trying it out if you need a quick cure primer.
Usually my priming method for poly helms is: degreasing soap wash with scotch pad, thin coat of Rustoleum universal bonding primer for optimal adhesion to the poly, then the Harbor Freight stuff for any scratch filling or general base coating. Then wet-sand and begin normal top-coats.
