PPPoE User Suddenly internet is not working even user is connected

Hi All, One of my clients is complaining to me sometimes, a pppoe user suddenly showing no internet at the user side but the user is connected with mikrotik pppoe server.. when he disconnects it from mikrotik and after re-connection, that user's internet is working fine at the user side.. So, is this related to the radius accounting response or something? Because this issue is not there when he is connected to a local user which is created in mikrotik without radius. Thanks Imdad