The only (and btw. fastest) way to properly sync Albums from Photos.App on the Mac to iOS Devices at the moment is to completely cancel all images from the Photo.App on the iOS devices (this may request 2-3 tries to really cancel all the pictures due to another Apple BUG) and completely resinc from Photos.app on the Mac to iPhone/iPadPro.
In my case (30K images) the result I get is a perfect sync.
The only problem is, I have to do this every time I add or cancel pictures from an album on one of the devices. If I do a normal Sync, the new pictures are not copied on the iOS Devices, and also the total amount of pictures is not correct. Some picutres are loosing without a reason. (in my case, at the moment: 33'881 (the real number) on the Mac, 24'486 on iPadPro, 31'961 on iPhoneX).
So be prepared: Every time you change (add/cancel pictures) your image collection in your albums Photos App, the only way to have the same content on all the Apple devices is to do a clean re-sync after deleting all the pictures on ior iOS device.
Don't expect any help on this form Apple, they just not care about user isussues or bugs, the care on demanding many monney for AppleCare....Apple doesn't care about you as an user, only about your monney.