Often, it's because of merging. Say Doe-12 was on the profile's biography, but then was merged into Doe-34. Both biographies get smooshed together, so no data is lost, but "Doe-12" is still written down in the biography. Hence it is red, because there is no Doe-12 any more.
It could also be because of a typo. Say the editor meant to type Doe-12, but instead typed Deo-12. "Deo-12" would be red, because Deo-12 does not exist.