playing ladder and my mercanry is equiped with Obedience, Guardian angels armor and tal rasha mask, hes frozen aura specced.

when meffisto frost nova him hes only frozen for like 0.5 sec or not at all, how is it possible when he has no can not be frozen item on ?

freeze duration depends not only on the source (the skill mephisto uses), but also on mods like "half freeze duration" and cold resist in general as well as the difficulty