On an Event record, the Registrant tab displays a list of those registered for the even and their statuses. This list can be filtered by status or name, among other filters. However, an event registrant is not appearing on the unfiltered list or on the list if filtered by last name. The registrant only surfaces when filtered by status.
Download and install the latest Service Pack which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.
Steps to Duplicate
Go to Events functional area
Search for the event
Select the Registrations tab
Clear any filters and observe the Registrant list, noticing constituents are missing
In the Registrant filter field type the name of the missing constituents and then apply
Observe that the constituent's record says, Attended = No
From the Attended drop-down filter, select No and then apply
Observe that the missing registrant now appears, Attended – No