[wdfifteen]

If you're getting fish eyes, either the surface is contaminated or you are using paints that are incompatible. It's most likely contamination.

To answer your last question, yes, something has changed. Silicone is really terrible for causing fish eyes, and it seems like silicone is everywhere anymore. It's gotten so that if I'm painting something that I haven't had in my possession for decades or otherwise KNOW it has no silicone on it, I start off with silicone remover. Silicone doesn't come off with soap and water, no matter how hard you scrub. You can get the real thing at an automotive paint store, or try acetone, toluene, or paint brush cleaner that has a whole concoction of nasty chemicals in it. After you get the obvious dirt off, go with the silicone remover, then grease remover. I hit it with the silicone remover again just to be sure. If you sand or sandblast silicone, you drive it into scratches in the metal or old paint and you'll never get it off.