If you are asking about the Cloud base version of Lightroom that is used on a real computer or the mobile version that is used on iOS and Android devices then LrC never synced with them. LrC syncs smart previews of images that are placed into collections that are synced with the WEB based system and then the mobile or other version of Lr syncs from/to that web base system.
In LrC open the preferences, go to the Sync tab, hold down the Alt key and clcik the button that says Rebuild Sync Data.
Or, if that doesn't fix your problem, Delete the CatalogNameSync.lrdata folder found in the same folder as your catalog file. You do that with LrC Closed of course.
There is no Lightroom CC. A few year ago Adobe did have a version that was called Lr CC because it was the Creative Cloud version that was in the subscription model. At that same time they also sold a perpetual licensed version that was called Lr 6.