If Photos app on your Mac freezes during sync process, most likely there is a large number of images in the library. However, this problem doesn’t depend on SyncMate directly, as the software uses the standard scripts provided by macOS to get an access to the Photos library albums.
The workaround is to create a new Photos Library and sync it anew.
To create a new Library follow the instructions:
1. Open Photos -> Preferences.
2. In Preferences click “Show in Finder” button.
3. In Dock right-click Photos and choose “Quit Photos”.
4. Archive the current library.
5. Move the archive to another location on your computer.
6. Delete your original library.
7. Launch Photos.
Please note that when you launch the app, you will receive an alert offering to “Open Library” or “Create new Library”. Choose “Create new Library” option.