Hey, @emelia3061866353ds. Welcome to the Lightroom Classic Community. I'll help you figure this out.
Syncing from Lightroom Classic can take slightly longer if the images have sets of masks and complex edits. Please check the current status at Lightroom Web (https://adobe.ly/3LUgRFj).
You can also click on the Sync Icons next to each collection to pause/stop syncing.

If you can locate the collection where these specific images are stored, start by adding flags or ratings to the photos and adding them to a new collection. Then, wait for this collection to finish Synchronizing.
Also, in Lightroom's Library Module> go to Library from the top menu > select 'Find all missing photos' and make sure none of the images are in a missing state with a (!), or a rectangular shape on the grid view. As images that are missing their originals won't sync up to the cloud. Head here to learn more: https://adobe.ly/3UGCppR
Let me know how it goes. Thanks!
Sameer K
(Type '@' and type my name to mention me when you reply)