It's called paint lift. It happens when there's not enough adhesion between the surface and the prime (adhesion promoter). Regardless of how well you prep it, the biggest culprit mainly comes from outdoor enviroment. Was it raining outside? Were you painting when there were plenty of humidity in the air? All this will cause it to lift. Next time you paint make sure it's clear/low humidy or find a place where there's a dehumidifier indoors. Of course, the only other place that have such thing would be a paint booth....
It sounds like you're painting trim pieces. If that's correct, then why are you using fabric and vinyl paint? Those are reserved for leather and cloth painting as they do not require any adhesive solution. Regular exterior auto paint or hi temp paint will do just fine.
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