Thanks for reaching out. We're sorry for the trouble with Lightroom. We're here to help.
Could you please share the version of Lightroom & the operating system you are working on? Has this started to happen recently? Have you newly imported a large batch of images in Lightroom? What format of photos do you work with, JPEG or RAW? Have you tried signing out of Lightroom & the Creative Cloud & sign in again?
Please try this;
Press the Alt key (Win) or Option key (Mac), and click the cloud icon in Lightroom > Click on View.
Check the images pending sync & apply flags/ratings to these images.
If there are any sync issues, click on them to know more, find the original for those images, and back them up safely before you empty the Sync issues from Lightroom Web. As long as there are sync issues on the Web, you can encounter trouble in syncing images & edits.
Hi I finally got this fixed with the help of Adobe support. On the web version of Lightroom I located the files that were causing the issue, deleted these files as I had a backup offline. Sync then worked. I believe that Lightroom does not handle sync from multiple devices very well - these were files I had previously moved from my camera to my phone. Hope this helps. -- Sent from Gmail Mobile