I have about 225 people in photos. One of those people is named Simon. There are about 200 photos of Simon. However, some of the photos of Simon show up later as "unknown." I will rename them Simon, but a couple days later, the photo says "unknown" again. This only happens with this one person (named Simon). Photos does not drop the name of any other person, only Simon.
iMac 27″ 5K, macOS 10.14
Hi cooperwidman,
When manually adding an identifier to the photos are you using the steps below found in the guide here?: Find and identify photos of people using Photos on Mac
"Manually identify and name people in a photo
Some photos may contain people who are not automatically named. You can name them manually.
on your Mac, double-click a photo to open it.
in the toolbar. Click the Add button 
, drag the circle to position it over the face if necessary, click the Name field, type a name, then press Return. multiple times to identify multiple faces in a photo. To remove a name that you added to a face, click the Remove button 
on the person.To stop showing face names in photos, choose View > Hide Face Names."
If so, do you use iCloud photos and do the changes show as expected on other devices? Find and identify people in Photos on iPhone
If the changes aren't syncing as expected after a normal restart, reach out to Apple Support directly to further assist.
Contact - Official Apple Support
Contact Apple for support and service - Apple Support
Best.
Photos is dropping people names and saying "unknown"
