When you search for a person reference, Mosaic returns all combinations of that person's names and addresses. If the number of results exceeds the value set in the findPersonTooManyMatches system property, you'll see ‘Too many matches. Please enter additional search criteria’ pop-up box.
You can try the following to resolve the pop-up notification:
Check if the number of names looks right. If you find any duplicate aliases you can delete, removing them will reduce the number of search results.
You can increase the value of the findPersonTooManyMatches system property to allow the results to display. There's no specific recommended value for this property but raising it lets Mosaic return larger result sets just keep in mind it might impact performance.