If there is problem with delivery of some of notifications (sorry I don’t understand your question, so this is my assumption) there should be some sign related to it in server log. If I were you I would download support archive (if this is managed installation) and check there for any related log entries. If there will be nothing like that, you may be forced to use some network tracing, but in general you should find there something. If log informations will not be enough for you, you can always create support ticket. Maybe there is some debug tracing that can be enabled.