Is this signature below your post still valid "MacBook Air 13", macOS 10.13"?
The strip of unnamed faces vanished with the upgrade to High Sierra, when Apple started to sync the faces with iCloud Photos Library. At that time the handling of faces changed considerably. It is now impossible to reject detected faces. We can no longer delete the faces of strangers or statues, or artefacts, that look like a face. So a list of unnamed faces will be pointless, because we can no longer weed it out. It will always she showing thousands of irrelevant faces. Looking for a face we want to name in this list will be like searching for a needle in a hay stack.
Photos will now initially only show a few people in the People album, for people, where it recognised the face at least 15 times in different photos (The limit of 15 is not documented - it is just an experimental result and appears in constants in the database files). When you name a face by typing a name into the name filed below the faces circle, the person should appear directly in the People album. Have you already enabled the option "View > Show Faces Names", so you can see the detected faces as an overlay, when you view a photo enlarged?
If you add a name to a face by typing the name into the circle below the face, but the person will not appear in the People album, this person may have been hidden.
To unhide the person and to a dd it back to the People album, try the following.
- Make the named faces visible with command "View > Show Faces"
- Find a photo of this person, where the face is circled, but the person is missing from the People album.
- Double click the photo to view it enlarged, then swipe up to show the "Details" section below the photo.
- There should be a face thumbnail in the "People" section of the Details. Double click this Face thumbnail to open the hidden People Album.
- In the open People album for this person scroll down, until you are seeing the command "Add to people Album". Click this, and the person should be back in the People Album.