I'll help you figure this out. What operating system are you working on? Have you recently imported a large batch of images into Lightroom?
Before you make any changes, log on to Lightroom Web (https://lightroom.adobe.com) & cross-check images that have successfully uploaded to the cloud.
If the images have synced up to the cloud, make a small change to existing images & check if that syncs up to the cloud.
Let me know how it goes.