I'll help you figure this out.
Where do you keep your images? On the internal drive or an external drive? Are you syncing Mask edits too? Does it work with a smaller group of images?
The images you're syncing edits to should not be missing. Try Syncing settings to some images that are stored on the internal drive. You can also try to use the Auto-Sync button to link a series of images.
Let me know how it goes,