There is a thread just below yours that was started a couple of years ago describing the same problem. As far as I can tell, there really isn't anything you can do about it if restarting Lightroom didn't do anything to resolve the issue. You don't have access to the index or the catalog. I would wait a while and see if the issue resolves itself. If it doesn't then there is a link on the main screen of the forum to report feedback. That link will get the attention of the developers more than this forum will.
I'd try to reset the local catalog, to see if that clears whatever problem exists in there. That involves deleting (using Finder when Lightroom is closed) the "Lightroom Library.lrlibrary" package, which you'll find in the user Pictures folder. After deleting it, starting Lightroom will cause it to be rebuilt from the cloud catalog, which will take a little while (depends on how many images you have in the cloud). Wait until the rebuild has finished (syncing has stopped and all albums/folders have been created and populated), then try to import again.
Oh boy thanks so much. Took me ages to find your posted solution, but this worked for me too. And it managed to solve the problem of 14 photos that simply would not synch and which I'd given up on. So thanks x 2.