My cured epoxy has a greasy film and the next coat won't stick, what happened?

That greasy, waxy film is almost certainly amine blush, a by-product that forms as epoxy cures in cool or humid conditions when the hardener reacts with moisture and carbon dioxide in the air. It is not a bad batch, and the cure underneath is usually perfectly sound. Blush is water-soluble, so the fix is simple: wipe the surface down with clean warm water and a scrubbing pad, dry it with a fresh cloth, then key it with an abrasive before recoating. Skipping that step is the usual reason a second coat or paint refuses to bond. Warming the workshop and keeping humidity down while it cures will cut down how much blush forms next time.