I seen versions of this issue before and it usually happens during an error when updating Network Calendars.
For example a client network calendar has a new/updated event, however the event cannot update the server network calendar, it can led to the newly created events being "lost" and although it is shown on the client Network Calendar, when you do a refresh the Event is no longer shown..
The most extreme versions of issue I have seen is the removal of all events, which is why I always keep the backup calendar turned on..
Version 1.0 had better online/offline event tracking and did not suffer from this concern, I have added a suggestion request for this feature ->
www.rainlendar.net/cms/index.php?option=com_joomlaboard&Itemid=27&func=view&id=720&catid=8