iCloud Photo Library: why isn't faces synced?

Apple said that in iOS11 and High Sierra face-data would be synced over iCloud. I was happy and tagged a lot of my people again (knowing it wouldn't dissapear again).

When i got my iPhone X I noticed that my library was downloading, but the people tab says its scanning for faces. But why? The date is allready in iCloud, i can be downloaded, right?

How is this feature really working and will I still have different faces on my iPhone and Mac, like on iOS10 and Sierra?