After migrating from Lightroom Classic CC, all my photo's have been synchronised to the cloud except for one. It keeps stating that one photo is still synchronising, but it never finishes. It's been stuck like this for several hours.
Maybe this has nothing to do with it, but during this time, my Lightroom Library file (wihout originals) did grow from 13GB to 17GB, but is now stable.
By comparing the number of photo's online and on my computer for each month, I eventually found the photo. After removing it and re-importing it, everything synced up. Problem solved!
Thanks. I had this same problem of just one photo that would not sync.Removing it from the LR Classic catalog and re-importing it fixed the problem.