People album not available while scanning in macOS Photos

On 10.14( Mojave) no pictures are available in the People album. There are ~81000 in my Photos library. Instead there is a notice:

"11,818 Photos Scanned. Photos will continue scanning your remaining 70064 photos when you're not using the app and your Mac is connected to power."

Also, scanning is very slow- overnight( about 8 hours) only 9000 pictures were scanned .

Why can I not see any photos in the People album and identify faces ?

In case it's important, it's the System Photo Library, although not the default name. And, the photos were imported by reference(i.e. not copied to the Photos Library).

There is a button, View People Album, below the notice but it is not selectable.