Photo app on Mac will not sync photos in iCloud Photo Library

I'm not sure about "Apple iPhotoLibrary" -- I'm guessing you mean the iCloud Photos Library? So the problem seems specific to the Mac.

So, can you tell us a bit more?

• Do you have more than one Photos Library on your Mac? 
• Where does your Mac's Photos Library reside-- in the Pictures folder of your internal drive, or on an external drive? or on a network? on iCloud drive?=
• …Do you have “Optimize Storage” checked in Photos’ Settings
• …Have you checked to see if the Apple Account is really really the same on the Mac and at iCloud.com?
• …Do you have more than 10% free storage on your iCloud account?
• What is your storage on this Mac? At System Settings>General> Storage, my Mac says 745 GB of 1TBB used. What does yours say? Is your  free storage on your Mac less than 10%?

Since syncing uses processing power, and people hate slow-downs, the Mac will avoid syncing while you use it. And since syncing requires bandwidth, the Mac will avoid syncing when the internet connection is weak.

So, if you want faster syncing, then you need good wifi, and keep the Mac turned on, probably over night. The Photos app should be turned off or left in the background.

Let us know some detail…

DrDanQ wrote:

1. Thank you for your reply,

Here are my answers:

yes I have more than one photo library....but the "proper one" IS selected

I'm not sure what you mean by "proper one." Is this Library designated as the System Library? You can check by closing Photos and option-clicking on the Photos icon to bring up the Library chooser.

2. it is on an external drive

How is this drive formatted? How is it connected? To avoid damaging the Photos Library an external drive must be formatted in either APFS format or Mac OS Extended (Journaled) format. The drive must be connected directly to the Mac by cable, not networked, clouded, NASed, etc. 

3. Optimize storage IS selected

4. apple accounts ARE the same

5. I have used 596GB out of 1 TB total

I'm guessing that this is on your Mac, and that's good-- lots of problems are caused by low storage. How about at iCloud?

Yep, 90K pictures is a lot! (Though it's not a record…) To speed things up, I have a smaller Library as the System Library and connected to iCloud-- it has just the pictures I want to share and show friends and family. I have other Libraries for archiving.

Do you leave the Mac running with Photos in the background at night?

OK. To narrow things down, try these steps:

• Restart the computer (of course)
• Re-start in Safe Mode. This bypasses certain potentially disruptive processes, and it often helps. Safe Mode is different for different computers, so see this: 

           Start up your Mac in safe mode - Apple Support 

• Make a new user and see if the same problem recurs with it.  This is a bit harder, because a new user can't access a different user's stuff. You would need to temporarily move your Library out of your own user's Pictuers folder up to the general "Users" folder. 
• Rebuild your Photos Library--close Photos and re-launch by option-command-clicking the app icon. If you use iCloud Photos, it’s possible that this will cause a re-sync that lasts long enough to make you nervous.
• I'd be tempted to try another Library. That is, to create a new Library by closing Photos and then option-clicking on the Photos icon. then see if the new Library will fill for iCloud.

The idea is to find out if the problem is with the Library, with your account, or with caches and login items, and stuff like that. One of these steps may fix the problem, but their failure to work also helps figure out what's happening.

Had you thought about dividing your large Library into smaller ones? Everything would be quicker. I have a "Favorites" Library for the pictures I want to share among my devices. Libraries for archives or special purposes stay separate.

Let us know what happens…

Also, there is the possibility that a file is not compatible and it's gumming up the works. See this:

Check the status of your library in Photos for macOS - Apple Support

Try making a Smart Album with

Photos is unable to upload and see if it lists anything.

Making a new Library and letting it fill from iCloud would insure a clean system.