Ive seen some posts about this several years old, so the solutions don't apply.
My Lightroom CC says syncing one photo. Its been this way for days. When I click "view" on the cloud icon there is nothing there. I did a diagnostics log and got it means little to me, though when I scrolled to "sync" I found the enclosed error. I put a copy of this file on my desktop, and deleted it from Lightroom and all other locations. I then reimported it and it did nothing. Ideas?