I have this problem with syncing 1 photo forever and considerably slowing down my computer. I tried the solution described in one post but when I press ALT and cloud it just opens the pop-up, not show the photo that's syncing. If I select sync status in filters it just shows:"Oh no! A black hole" so apparently no photo is syncing. What can I do to make Lightroom usable again?
Lightroom doesn't have any issues on my mobile phone or the web version but when I open the desktop version my whole computer starts freezing and the syncing of that one imaginary photo doesn't stop. I left it overnight and in the morning it was still syncing. I need help with this because for me Lightroom is unusable right now and I have no idea what to do.
Have you checked the "Deleted" section below All Photos. Open that section and see if any one of the deleted images is still showing the "sync in progress" icon. If so, permanently delete that item and that should fix the syncing issue.