Here is the solution if your ‘My Photo Stream’ iCloud Apple Photos App feature is not working correctly.
- You have sign in your iCloud Account on Your Mac
- My Photo Stream is selected & Active inside your System Preferences > iCloud > Photos App Settings
- Quit the Photos App if it’s running
- Launch the Activity Monitor located in Applications > Utilities > Activity Monitor
- In Activity Monitor search for ‘photos’ in search toolbar in ‘CPU’ Tab
- Locate & Select ‘Photos Agent’ process & click ‘X’ at top left to quit that process
- On confirmation message click ‘Force Quit’ to end the process
- You can quit Activity Monitor
- Open Photos App again, Your My Photo Stream should be working as normal.
I hope this information helps,
Thanks & Regards