In Lightroom Classic, when adding a virtual copy (VC) to a collection that is synced, or syncing a collection containing a VC after creating the collection, the VC will not sync. The only way to get a VC to sync from LR Classic is to create the VC after its template (whether a master or a previously-created VC) is already in the collection. Thus for example, create a new collection in LR Classic. Sync it now or sync it after adding an existing VC. The collection will be created in LR CC, but it will be empty. Now make a VC of the VC. The LR Classic collection now contains two images. Only the newly-created VC will sync with LR CC. Obvioiusly syncing an existing collection in LR Classic should sync 100% of the images in that collection, regardless of whether master or VC, regardless of when the VCs were created.