Advice for working with polyurethane?

i am using water based polyurethane on a decoupage project, and in spots, the finish is cloudy. at first, i was at the bottom of a can, and so i bought a new can of the same type, and the new can is putting cloudy finish in spots. when i run my hand on it, it’s not bubbly, it’s just when you look at the finish in the light, you see areas where it appears duller or not shiny. does anyone know anything about polyurethaning?