Amine blush appears as a waxy coating on the surface of cured epoxy. Sanding does not remove amine blush, it just pushes it around on the surface. You should assume that ANY epoxy can have an amine blush after curing, even if the label indicates it is non-blushing. Any surface blush must be removed before you apply additional coats of epoxy, varnish, or paint, otherwise the finished surface will not cure properly, or bond to the substrate as intended.
Use a Scotch-Brite abrasive pad and water (not solvent) to remove amine blush; change the water regularly to ensure all blush byproduct is removed completely. A mild soap can be added to the water, if desired, but strong detergents or specialty soaps are not required. Rinse surface thoroughly, and allow the surface to dry.