I use iCloud software for Windows 7 (with the latest update).
GOOD: My old iPhone 6s+ photos are all downloaded to iCloud PC app.
PROBLEM: New iPhoneX (iOS 12.0.1) pics do not sync (few thousand of them). If I try to redownload pics from 2018, it only downloads 6s+ photos again and then it stops.
HELPFUL INFO: 1. ALL my pics are visible on iCloud on the web.
In Windows iCloud app:
- My Photo Stream is not selected
- iCloud Photo Libarary, Download new Photos and Keep High efficiency original are selected.
On iPhone X: iCloud Photos is clicked, Optimise iPhone Storage is selected, Download and keep originals is not and Upload to my Photo Stream is not. Shared Albums is on (though I don't use it).
(I no longer use the old iPhone, but preserved the same iCloud account)