Call made to LyncClient Automation BeginStartConversation, callback not received in certain cases

Hello,

I have observed that when I restart Windows and then Lync client after sleep/ hibernate, then sometimes the callback is not invoked

Here is my code

IAsyncResult ar = LyncClient.GetAutomation().BeginStartConversation(AutomationModalities.InstantMessage, ptcpts, _ModalitySettings, ConversationWindowCreatedCallback, null);

ConversationWindowCreatedCallback is not invoked . Sometimes Lync signout- sigin is required to get it working. This issue is observed in a customer environment not in development environment.