Issue:
When viewing a report, some of the rows are presenting no data at all and are completely empty.
Cause:
In campaign studio, contacts that are not yet identified fully, known as "anonymous contacts" are tracked so that any data found for them can be associated with their email address once it is identified. Because of this preemptive tracking, reports will sometimes show information for contacts that do not yet have any relevant identifiers associated with them, and will show up as blank for most columns
Workaround:
The best way around this is to simply add a filter to your report for Email:exists, this will keep anonymous contacts out of the report until they have been associated with an email address.