Please review the following in order until resolved: 

1. Process the event registration transaction in the NetCommunity plug-in in The Raiser's Edge. Unprocessed transactions will not show on the attendee list. 

2. The event attendee list in NetCommunity will only display the participants that have opted in to be displayed on the list. If the attendee list opt-in attribute is missing from the participant's record, they will not be included on the attendee list in NetCommunity. For more information on how to set up the attendee list, please refer to our article How to create a see who's coming list for event registration forms.  (Note: The Directory Part setting for "Records to Include" does not apply when using the part for an event attendee list if a query is present. The attendee list results are controlled only by the opt-in participant attribute added to the participant records in The Raiser's Edge.) 

3. The event attendee list uses a Directory part. When the part/lists first loads, the first 500 results will list. Use the search fields to find an attendee if there are more than 500 registered and listed for the event. For more information, please refer to Directory search (Event Attendee List) only shows results of up to 500